Composite pipe

ABSTRACT

A pipe comprises a pipe wall formed of a composite material of a matrix and a plurality of reinforcing fibres embedded within the matrix, wherein the composite material in at least one region of the pipe wall is pre-stressed. The composite material in at least one region of the pipe wall comprises or defines at least one of a level of pre-tension and pre-compression.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to PCT Patent Application No.PCT/GB2011/001686 filed on 5 Dec. 2011, which claims priority to UnitedKingdom Patent Application No. GB1020509.4 filed on 3 Dec. 2010, thecontents of which are incorporated herein by reference.

BACKGROUND

Composite pipes are used in many industries, such as in the oil and gasindustry for the confined transportation of fluids and equipmentassociated with hydrocarbon recovery from a subterranean reservoir. Forexample, composite marine risers, flow lines and jumpers are known inthe art.

WO 99/67561 discloses a flexible composite pipe which is intended foruse in transporting fluids such as hydrocarbons, and is formed frommultiples coaxially aligned discrete layers which are bonded to eachother. Specifically, the disclosed prior art pipe comprises separateinner and outer layers, and one or more discrete intermediate layerswhich include reinforcing fibres and which are disposed between theinner and outer liners.

SUMMARY

A pipe having a pipe wall may comprise a composite material formed of atleast a matrix and a plurality of reinforcing fibres embedded within thematrix, wherein at least one circumferential segment of the pipe wallcomprises or defines a local variation in construction to provide alocal variation in a property of the pipe.

According to a first aspect of the present invention there is provided apipe having a pipe wall comprising a composite material formed of atleast a matrix and a plurality of reinforcing fibres embedded within thematrix, wherein in a plane which extends laterally through the pipe wallthe matrix material defines a continuous circumferential structure andat least one circumferential segment of the pipe wall in said lateralplane comprises or defines a local variation in construction to providea local variation in a property of the pipe.

One circumferential segment of the pipe wall may define a localvariation in construction relative to a different circumferentialsegment to provide a local variation in a property of the pipe.

The matrix material defines a continuous circumferential structure suchthat the matrix does not include any discontinuities, such as windows orthe like, which extend through the entire thickness of the pipe wall. Assuch, at least the matrix defines a complete structure around a bore ofthe pipe sufficient to provide, for example, fluid containment at leastat the defined lateral plane.

The pipe wall may comprise at least two circumferential segments havingdifferent constructional properties.

The pipe wall may define a global construction around its circumference,wherein at least one circumferential segment comprises a local variationwithin this global construction.

Thus, the construction of the pipe wall includes one or more localvariations around its circumference to achieve a local variation in aproperty of the pipe. That is, the constructional variation issufficient to affect a variation in a property of the pipe.

In use, the local variation in a property of the pipe by virtue of thelocal constructional variation in at least one circumferential segmentmay establish a preferential characteristic in the pipe. Such apreferential characteristic may beneficially differ from that in a pipeof uniform circumferential construction. A preferential mechanicalcharacteristic may be achieved, such as a strength, stiffness, flexuralrigidity, bending, resonant characteristic or the like. A preferentialthermal characteristic may be achieved, such as a thermal expansioncharacteristic, thermal insulation characteristic or the like.

The local constructional variation in at least one circumferentialsegment may establish a preferential characteristic affecting the pipein a longitudinal direction. For example, the local constructionalvariation in at least one circumferential segment may establish apreferential longitudinal stiffness distribution or variation. Such apreferential longitudinal stiffness may permit a predetermined bendingor flexing motion of the pipe to be achieved. Although discussed againand in further detail below, such predetermined bending may facilitatecoiling of the pipe, desired compliance of the pipe during installation,controlled deformation during expansion and contraction of the pipe,controlling circumferential orientation of the pipe and the like.

The circumferential segment may extend between inner and outer surfacesof the pipe wall. An entire circumferential segment of the pipe wall maydefine a local variation in construction. A portion within at least onecircumferential segment may define a local variation in construction.For example, at least one circumferential segment may comprise a localvariation in construction at a location intermediate inner and outersurfaces of the pipe wall.

At least one circumferential segment may comprise a local variation inmodulus of elasticity. At least one circumferential segment may comprisea local variation in second moment of area. At least one circumferentialsegment may comprise a local variation in coefficient of thermalexpansion. At least one circumferential segment may comprise a localvariation in thermal conductivity. At least one circumferential segmentmay comprise a local variation in a material strength, such as a yieldstrength of a particular component of the composite material. At leastone circumferential segment may comprise a local variation in tensilestrength. At least one circumferential segment may comprise a localvariation in hoop strength. At least one circumferential segment maycomprise a local variation in compressive strength. At least onecircumferential segment may comprise a local variation in flexuralstrength.

The local constructional variation in at least one circumferentialsegment of the pipe wall may define a discrete constructional variation,for example with respect to an adjacent region or segment. For example,the local constructional variation may be provided in a step-wise orabrupt manner with respect to an adjacent region.

The local variation in at least one circumferential segment of the pipewall may comprise a tapered or gradual variation, for example withrespect to an adjacent region or segment.

At least one circumferential segment may comprise a local variation inthe construction of the composite material, such as a constructionalvariation in one or both of the matrix material and the reinforcingfibres.

At least one circumferential segment may comprise a local variation inthe type of matrix material. At least one circumferential segment maycomprise a local variation in the volume of matrix material.

At least one circumferential segment may comprise a local variation inthe distribution density of the reinforcing fibres within the matrixmaterial. For example, the reinforcing fibres may be more densely packedtogether in at least a portion of one circumferential segment of thepipe wall than another circumferential segment. In such an arrangementthe region of increased fibre packing density may define a region ofmodified stiffness, such as increased stiffness.

At least one circumferential segment may comprise a local variation inthe type of fibre within the composite material. That is, at least aportion of one circumferential segment of the pipe wall may comprise afibre type which is not present in another circumferential segment, orat least present in a different quantity or configuration. At least onecircumferential segment may comprise one or more fibres with a modified,such as increased or decreased, stiffness, tensile strength, compressivestrength or the like. At least one circumferential segment may compriseone or more reinforcing fibres with a modified dimension, such as amodified diameter. For example, at least a portion of onecircumferential segment of the pipe wall may comprise fibres having adifferent diameter to those in a different circumferential segment.

At least one circumferential segment may comprise a local variation infibre alignment angle within the composite material. That is, one ormore reinforcing fibres in at least a portion of one circumferentialsegment may define a different alignment angle to one or morereinforcing fibres in a different circumferential segment. In thisarrangement the fibre alignment angle may be defined relative to thelongitudinal axis of the pipe. For example, a fibre provided at a 0degree alignment angle will run entirely longitudinally of the pipe, anda fibre provided at a 90 degree alignment angle will run entirelycircumferentially of the pipe, with fibres at intermediate fibrealignment angles running both circumferentially and longitudinally ofthe pipe, for example in a spiral pattern.

The local variation in fibre alignment angle may include fibres havingan alignment angle of between, for example, 0 and 90 degrees, between 0and 45 degrees or between 0 and 20 degrees.

In one arrangement at least one circumferential segment may comprise alocal variation in fibre alignment angle in which one, or morepreferably a plurality of fibres define an alignment angle ofsubstantially 0 degrees.

At least one circumferential segment of the pipe wall may comprise alocal variation in fibre pre-stress. In this arrangement the fibrepre-stress may be considered to be a pre-stress, such as a tensilepre-stress and/or compressive pre-stress applied to a fibre duringmanufacture of the pipe, and which pre-stress is at least partially orresidually retained within the manufactured pipe. In this arrangementthe fibre pre-stress in one circumferential segment of the pipe wall maydiffer from that in a different circumferential segment. In onearrangement the fibre pre-stress, such as pre-tension, in at least onecircumferential segment of the pipe wall may be increased relative to adifferent circumferential segment. A local variation in fibre pre-stressmay permit a desired characteristic of the pipe to be achieved, such asa desired bending characteristic. This may assist to position ormanipulate the pipe, for example during installation, retrieval, coilingor the like. Further, this local variation in fibre pre-stress mayassist to shift a neutral position of strain within the pipe wall, whichmay assist to provide more level strain distribution when the pipe is inuse, and/or for example is stored, such as in a coiled configuration.

At least one circumferential segment may comprise a local variation inconstruction by use of at least one insert. The insert may be consideredto be a separate component from the matrix and reinforcing fibres whichform the composite material of the pipe wall. The insert may be formedseparately and subsequently installed within at least onecircumferential segment of the pipe wall. An insert may be installedwithin the pipe wall during manufacture of the pipe. An insert may beinstalled within the pipe wall following manufacture of the pipe.

Any insert may not extend through the entire thickness of the pipe wall,at least at the lateral plane, as such an arrangement would result inthe matrix material becoming discontinuous.

The insert may define a structural insert. The insert may exhibitsufficient mechanical properties, such as stiffness, strength or thelike, to provide a measurable effect on the mechanical properties of theentire pipe. For example, a single strand of a reinforcing fibre may notfunction as an insert due to the magnitude of difference between thestructural properties of a single strand and the entire pipe. At leastone insert may comprise an elongate insert. At least one insert mayextend substantially longitudinally of the pipe. At least one insert maycomprise a plate, rod, pin or the like. At least one insert may comprisea mesh structure or the like. At least one insert may comprise ametallic material, such as a metal alloy. At least one insert maycomprise a shape memory metal alloy. At least one insert may comprise anon-metallic material. At least one insert may comprise a compositematerial, such as a composite of a matrix with embedded reinforcingfibres. In this arrangement a composite insert may be formed separatelyand subsequently installed or included in at least one circumferentialsegment of the pipe wall.

At least one circumferential segment may comprise a local variation ingeometry. For example, at least one circumferential segment may definean increased or reduced wall thickness of the pipe wall.

At least one circumferential segment comprising a local constructionalvariation may extend longitudinally of the pipe. This arrangement maypermit the local circumferential variation to desirably affect the pipein a longitudinal direction.

At least one circumferential segment comprising a local constructionalvariation may extend longitudinally of the pipe parallel to the pipeaxis. In this embodiment the circumferential location of at least onesegment may be constant over a length of the pipe.

The location of at least one circumferential segment comprising a localconstructional variation may extend both longitudinally andcircumferentially of the pipe. In such an arrangement a localcircumferential variation may extend in a spiral arrangement along alength of the pipe.

A local constructional variation in at least one circumferential segmentof the pipe wall may remain constant along a length of the pipe. In thisarrangement a common effect of the local constructional variation may beprovided over a length of the pipe.

A local constructional variation in at least one circumferential segmentof the pipe wall may vary along a length of the pipe. In thisarrangement a variable effect of the constructional variation may bepresented over a length of the pipe.

The local constructional variation in at least one circumferentialsegment may be selected to provide a desired longitudinal bendingcharacteristic along the pipe. For example, the local constructionalvariation in at least one segment may be selected to providelongitudinal bending in a desired plane. This arrangement may permit arepeatable bending motion to be achieved, which may assist in coiling ofthe pipe, for example during deployment and retrieval, installation ofthe pipe or the like. This arrangement may also, or alternatively,permit multiple pipes according to the present aspect of the inventionto be arranged in proximity to each other, wherein the localconstructional variation in each pipe facilitates controlledlongitudinal bending, for example in a preferred plane, which is adaptedto prevent or substantially minimise interference between the pipes.This may be of concern where, for example, multiple pipes are bundled ina common location, extend along a common path or course, converge to acommon restricted location from various directions or the like.

Such a desired longitudinal bending characteristic may be achieved byproviding a local variation in stiffness within at least onecircumferential segment of the pipe. In some embodiments a variation instiffness, for example an increase in stiffness, within at least onecircumferential segment may permit stresses within the pipe duringlongitudinal bending to be reduced.

The local constructional variation in at least one circumferentialsegment may be selected to provide a desired deformation characteristic,such as bending, buckling or the like, within the pipe when under load,such as when exposed to internal pressure, external pressure, torsionalloading, radial loading, axial loading or the like. For example, thepipe may be formed to permit bending or deformation to be restricted toa particular direction or plane.

The local constructional variation in at least one circumferentialsegment may be selected to provide a desired longitudinal twistcharacteristic of the pipe. For example, the local constructionalvariation may permit the pipe to be deployed and retrieved, for exampleby coiling or spooling, while achieving a desired rotational orientationof the pipe. Such an arrangement may permit, for example, the pipe toadopt a desired orientation when deployed or retrieved, which may inturn permit supported equipment, for example, to also be deployed orretrieved in a desired orientation. Further, such control over theorientation of the pipe by virtue of a selected local constructionalvariation may facilitate more accurate measurement processes associatedwith the pipe, such as NDT testing, strain measurements and the like. Inthis respect, knowledge that the pipe will be orientated in a particulardirection may assist in the positioning of measurement equipment,eliminate or minimise the requirement to separately determine theorientation of the pipe during measurement, or the like.

The local constructional variation in at least one circumferentialsegment may be selected to provide a desired thermal characteristic ofthe pipe.

The local constructional variation in at least one circumferentialsegment may be selected to provide a desired thermal expansion and/orcontraction characteristic of the pipe. For example, a localconstructional variation may be selected to permit the pipe to deform ina repeatable and expected manner upon thermal expansion thereof. Thismay, for example, permit controlled buckling of the pipe to be achievedduring thermal expansion.

The local constructional variation in at least one circumferentialsegment may be selected to provide a desired thermal insulationcharacteristic of the pipe. For example, a variation in thermalconductivity within a circumferential segment of the pipe wall maypermit a desired thermal insulation property to be achieved within saidsegment. This may be advantageous in circumstances where differentcircumferential segments of the pipe are exposed to different conditionswhen in use. For example, in one embodiment a portion of the pipe may beburied, for example in a seabed, and a portion may be exposed to anambient environment, such as the sea. In such an exemplary arrangementthe circumferential segment of the pipe which is exposed to the ambientenvironment may be locally modified to exhibit greater thermalinsulation properties that that segment which is buried. This may permitthe pipe to be more accurately formed for its intended use.

The local constructional variation in at least one circumferentialsegment may be selected to provide a desired thermal transmissioncharacteristic of the pipe. This arrangement may, for example, permitheat, which may be provided from a heater, to be transmitted through thewall of the pipe. This may facilitate application in which an externalheater is used to heat fluids within the pipe.

The pipe may comprise at least two circumferential pipe wall segmentswhich each comprise a local variation in construction to provide a localvariation in a property of the pipe. Each of the at least twocircumferential segments of the pipe wall may comprise the same ordifferent constructional variations.

The pipe may comprise two circumferential segments having a localconstructional variation which are arranged substantially diametricallyopposite each other. This arrangement may permit a desired property ofthe pipe to be achieved within or relative to a desired plane. In onearrangement the two segments may each comprise a local constructionalvariation to provide a local variation in stiffness longitudinally ofthe pipe. For example, each segment may define a region of increasedstiffness such that the bending stiffness within the plane whichincludes both circumferential segments is increased. In such anarrangement the two circumferential segments with increased stiffnessmay define a neutral bending plane along which the pipe will bend.Accordingly, controlled bending orientation of the pipe may be achieved,which may assist in spooling, installation, during service or the like.Providing an effective increased stiffness along a bending plane maypermit a reduction in the stresses developed within the regions of lowerstiffness located at a distance from the neutral bending plane. This maytherefore increase safety, and may, for example, permit a reducedpermissible spooling diameter of the pipe to be achieved. It should beunderstood that a similar effect may be achieved by providing a localreduction in stiffness, such as axial stiffness, at two diametricallyopposed circumferential segments.

The matrix of the composite material may define a continuous structure,wherein the reinforcing fibres are embedded within said continuousstructure. In this arrangement the composite material may effectively beprovided as a single layer throughout the thickness of the pipe wall,without any interfaces, such as bonded interfaces, between individuallayers.

The distribution of the reinforcing fibres may vary throughout thecontinuous matrix in a radial direction through the pipe wall. Thedistribution of the reinforcing fibres may vary from zero at the regionof the inner surface of the pipe wall, and be increased in a directiontowards the outer wall. Accordingly, the region of the inner surface ofthe pipe wall will be absent of reinforcing fibres.

A radially inner region of the pipe wall may define a uniformconstruction, and a radially outer region of the pipe wall may compriseat least one circumferential segment which comprises or defines a localvariation in construction. That is, the radially outer region maycomprise at least two circumferential segments having a constructionalvariation therebetween. This arrangement may be achieved duringmanufacture of the pipe by providing a pre-formed pipe structure ormandrel of uniform construction and which defines the radially innerregion of the pipe wall, and then forming the radially outer pipe wallregion on the pre-formed mandrel, while including a variation inconstruction in one circumferential segment.

A method of manufacturing a pipe may comprise:

forming a pipe wall with a composite material comprising a matrix and aplurality of reinforcing fibres embedded within the matrix; and

creating a local variation in the construction of the pipe wall withinat least one circumferential segment of the pipe wall to provide a localvariation in a property of the pipe.

According to a second aspect of the present invention there is provideda method of manufacturing a pipe, comprising:

forming a pipe wall with a composite material comprising a matrix and aplurality of reinforcing fibres embedded within the matrix, wherein thematrix material defines a continuous circumferential structure in aplane which extends laterally through the pipe wall; and

in the same lateral plane creating a local variation in the constructionof the pipe wall within at least one circumferential segment thereof.

The method may comprise forming a pipe in accordance with the firstaspect. Features defined above in relation to the first aspect may alsobe associated with the second aspect.

A pipe may have a pipe wall comprising a composite material formed of atleast a matrix and a plurality of reinforcing fibres embedded within thematrix, wherein the composite material in at least one region of thepipe wall is pre-stressed.

According to a third aspect of the present invention there is provided apipe having a pipe wall comprising a composite material formed of atleast a matrix and a plurality of reinforcing fibres embedded within thematrix, wherein the composite material comprises a varying level ofpre-stress between different regions of the pipe wall.

Thus, in the third aspect the pipe may comprise a plurality of regionswithin the pipe wall, wherein a level of pre-stress within the compositematerial varies between at least two regions.

The composite material in at least one region of the pipe wall maycomprise or define a level of pre-tension.

The composite material in at least one region of the pipe wall maycomprise or define a level of pre-compression.

Pre-stress may be applied to the composite material within at least oneregion of the pipe wall during manufacture of the pipe. Such apre-stress applied during manufacture may remain, at least residually,within the pipe wall region following manufacture.

Pre-stress within the composite material of at least one region of thepipe wall may be achieved by applying a tension to one or more of thereinforcing fibres of the composite material during manufacture of thepipe. Such applied tension may introduce a level of strain within one ormore of the reinforcing fibres of the composite material duringmanufacture of the pipe. In one embodiment a 0.05 to 0.5% strain withinone or more of the reinforcing fibres may be applied during manufactureof the pipe. A variable tension may be applied to one or more of thereinforcing fibres of the composite material during manufacture of thepipe.

Pre-stress may be achieved by applying a compression to one or morefibres during manufacture of the pipe.

In one embodiment a region of the pipe wall may be formed using anelongate composite tape, roving, tow or the like which is manipulated,for example wound, to form the pipe wall. In such an arrangementpre-stress may be applied within the elongate composite tape, roving,tow or the like during manufacture of the pipe. For example, a definedtension or compression may be applied to the elongate tape, roving, towor the like during manufacture. A variable tension or compression may beapplied to the elongate tape, roving, tow or the like during manufactureto establish different regions of the pipe wall with different levels ofpre-stress.

Pre-stress within the composite material in at least one region of thepipe wall may be provided to achieve a desired stress and/or straindistribution within the pipe wall when the pipe is exposed to ananticipated condition.

Such an anticipated condition may be a condition when the pipe is in aservice configuration, such as when exposed to internal and/or externalfluid pressure and associated stresses and strains, such as hoopstresses/strains and the like. In such an arrangement the pre-stresswithin the composite material in at least one region of the pipe wallmay be provided to achieve desired burst and/or collapse properties,such as strengths, of the pipe.

An anticipated condition may comprise a condition when the pipe is in astorage configuration, such as in a coiled storage configuration whichmay produce bending stresses/strains, axial tensile and compressivestresses/strains, torsional stresses/strains and the like. Ananticipated condition may comprise a deployment configuration, such asthe deployment from a reel, a retrieval configuration, such as retrievalonto a reel, or the like.

In one embodiment pre-stress within the composite material in at leastone region may be provided to establish a desired stress and/or straindistribution within the pipe wall when the pipe is exposed to aparticular or anticipated condition. Such a desired stress and/or straindistribution may include a more even or improved distribution throughoutthe pipe wall, for example when compared to a conventional compositepipe. Such a more even or improved stress and/or strain distribution mayassist to minimise failure frequency, material fatigue, permit controlor reduction in crack propagation, and the like. Further, such a moreeven or improved stress and/or strain distribution may permit higherstrengths within the pipe wall to be achieved for given quantities ofmaterial.

Pre-stress within the composite material in at least one region of thepipe wall may be provided to achieve a desired movement bias of thepipe, such as a desired bending movement, buckling movement, elongationmovement, radial expansion movement or the like.

The provision of a pre-stress within the composite material in at leastone region may function to alter a neutral position of strain within thepipe wall.

The variation in pre-stress between different regions of the pipe wallmay provide a desired global stress and/or strain distribution withinthe pipe wall when the pipe is exposed to a particular or anticipatedcondition, such as a service condition or the like. For example, thevariation in pre-stress between the different regions may provide a moreeven or improved global stress and/or strain distribution within thepipe wall when exposed to a particular condition, such as a servicecondition or the like. A variation in the level of pre-stress betweendifferent regions of the pipe wall may permit a neutral position ofstrain within the pipe wall to be desirably affected, for example toaccommodate a particular service condition or the like.

A variation in pre-stress within the composite material betweendifferent regions of the pipe wall may be provided in an abrupt orstep-wise manner.

A variation in pre-stress within the composite material betweendifferent regions of the pipe wall may be provided in a gradual ortapered manner.

The pipe may comprise a plurality of regions within the pipe wall,wherein the composite material in at least one region may bepre-stressed, and the composite material in at least one other regionmay define or comprise substantially zero pre-stress. In such anarrangement a variation in composite material pre-stress between twodifferent regions may vary from a neutral level of pre-stress.

A variation in pre-stress within the composite material betweendifferent regions may be provided by a combination of pre-tension andpre-compression within different regions.

A level of pre-stress present in the composite material in one region ofthe pipe wall may establish or influence the level of pre-stress createdor provided in a different region of the pipe wall.

A pre-stress applied within the composite material of one region of thepipe wall may be selected to provide a particular pre-stress in afurther region of the pipe wall. For example a degree of pre-stress inthe form of tension applied in the composite material in one region ofthe pipe wall may provide a degree of pre-stress in the form ofcompression in the composite material in a different region of the pipewall. Further, a degree of pre-stress in the form of tension applied inthe composite material in one region of the pipe wall may provide alower level of pre-tension in the composite material in a differentregion of the pipe wall.

The level of pre-stress within the composite material of the pipe wallmay vary throughout the pipe wall in a radial direction. That is, thelevel of pre-stress within the composite material may vary throughoutthe thickness of the pipe wall. For example, the composite material inan outer region or layer of the pipe wall may comprise or define adifferent level of pre-stress than the composite material in an innerregion or layer of the pipe wall. The outer region may entirelycircumscribe the inner region.

The composite material in an outer region of the pipe wall may compriseor define a level of pre-tension, and the composite material in an innerregion of the pipe wall may comprise or define a level ofpre-compression. In this arrangement the pre-tension applied in thecomposite material of the outer region of the pipe wall may establishthe pre-compression, or at least a portion of the pre-compression,within the composite material of the inner region of the pipe wall. Forexample, the pre-tension applied in the composite material of the outerregion may apply a compressive hoop strain in the composite materialwithin the inner region. This arrangement may be advantageous inapplications where internal pipe pressures are dominant.

The composite material in an inner region of the pipe wall may compriseor define a level of pre-tension which is greater than that in an outerregion of the pipe wall. This arrangement may be advantageous inapplications where external pipe pressures are dominant.

A variation in pre-stress within the composite material in a radialdirection of the pipe wall may be selected in accordance with one ormore anticipated service conditions of the pipe. For example, a radialvariation in hoop and/or axial pre-stress may be selected in accordancewith one or more anticipated service conditions of the pipe. Theprovision of a variation in the pre-stress within the composite materialin a radial direction of the pipe wall may, for example, be configuredto accommodate stresses and/or strains applied to the pipe when exposedto internal and/or external pressures. Such accommodation of pressureapplied stresses and strains may be in order to ensure a more evenstress and/or strain distribution throughout the pipe wall.

For example, in an anticipated service condition in which internalpressures are dominant, for example when the product of the internalpressure and the inner radius of the pipe is higher than the product ofthe external pressure and the outer radius of the pipe, the resultanthoop stresses will be tensile. Accordingly, the composite materialwithin an inner region will typically be exposed to a greater tensilestrain than the outer region. As such, with increasing load as a resultof increasing internal pressure, a failure strain level may be achievedfirst in the inner region. However, by provision of pre-tension in anouter region of the pipe wall which has the effect of applying apre-compression within the composite material of the inner layer, theinner layer may be permitted or enabled to support a greater degree ofstrain before a failure strain limit is reached.

Conversely, in an anticipated service condition in which externalpressures are dominant, the resultant hoop stresses will be compressive.The present invention may accommodate such a service condition byproviding a greater degree of pre-tension in the composite material inthe inner region of the pipe wall than in the outer region.

The level of pre-stress within the composite material of the pipe mayvary throughout the pipe wall in a longitudinal direction. For example,the composite material in one longitudinal region of the pipe wall maycomprise a different level of pre-stress from the composite material ina different longitudinal region of the pipe wall. Such an arrangementmay be advantageous in circumstances where the pipe load requirementsvary along the length of the pipe. For example, one longitudinal regionof the pipe may be required to support a greater load, for example anaxial load, than a different longitudinal region.

The level of pre-stress within the composite material of the pipe mayvary throughout the pipe wall in a circumferential direction. Forexample, the composite material in one circumferential region or segmentof the pipe wall may comprise a different level of pre-stress from thecomposite material in a different circumferential region or segment ofthe pipe wall. This arrangement may permit a variation in a property ofthe pipe in a circumferential direction to be achieved. Such anarrangement may permit a desired bending of the pipe, for example, to beachieved in a repeatable manner.

The modulus of the composite material may be varied throughout the pipewall. The modulus of the composite material may be varied by varying themodulus of the matrix, for example by varying the type of matrixmaterial. The modulus of the composite material may be varied by varyingthe modulus of one or more reinforcing fibres, for example by varyingthe type of reinforcing fibre.

The modulus of the composite material may be varied by varying thealignment angle of the reinforcing fibres. The fibre alignment angle maybe defined relative to the longitudinal axis of the pipe. For example, afibre provided at a 0 degree alignment angle will run entirelylongitudinally of the pipe, and a fibre provided at a 90 degreealignment angle will run entirely circumferentially of the pipe, withfibres at intermediate fibre alignment angles running bothcircumferentially and longitudinally of the pipe, for example in aspiral pattern.

The modulus of the composite material may be varied in a radialdirection within the pipe wall.

In one arrangement one or more fibres located within an outer region ofthe pipe wall may define a greater fibre alignment angle than one ormore fibres located within an inner region of the pipe wall. Forexample, one or more fibres in an outer region of the pipe wall maydefine a fibre alignment angle in the region of 75 to 90 degrees, andone or more fibres in an inner region of the pipe wall may define afibre alignment angle in the region of 65 to 80 degrees. In such anembodiment the inner fibres aligned at a lower alignment angle may becapable of accommodating higher hoop strains than the outer fibresaligned at a greater alignment angle. Such an arrangement may beadvantageous in conditions where internal and/or external pressures aredominant.

In an alternative arrangement one or more fibres located within an innerregion of the pipe wall may define a greater fibre alignment angle thanone or more fibres located within an outer region of the pipe wall. Suchan arrangement may be advantageous in combined load conditions, axialloading, bending moments, pressure loading or the like.

The matrix of the composite material may define a continuous structure,wherein the reinforcing fibres are embedded within said continuousstructure. In this arrangement the composite material may effectively beprovided as a single layer throughout the thickness of the pipe wall,without any interfaces, such as bonded interfaces, between individuallayers.

The distribution of the reinforcing fibres may vary throughout thecontinuous matrix in a radial direction through the pipe wall. Thedistribution of the reinforcing fibres may vary from zero at the regionof the inner surface of the pipe wall, and be increased in a directiontowards the outer wall. Accordingly, the region of the inner surface ofthe pipe wall will be absent of reinforcing fibres.

A radially inner region of the pipe wall may define a uniform level ofpre-stress, and a radially outer region of the pipe wall may define avarying level of pre-stress. That is, the radially outer region maycomprise at least two sections having different levels of pre-stress.This arrangement may be achieved during manufacture of the pipe byproviding a pre-formed pipe structure or mandrel of uniform pre-stressdistribution and which defines the radially inner region of the pipewall, and then forming the radially outer pipe wall region on thepre-formed mandrel, while including a variation in pre-stress in theradially outer region.

A method of manufacturing a pipe may comprise:

forming a pipe wall with a composite material comprising a matrix and aplurality of reinforcing fibres embedded within the matrix; and

pre-stressing the composite material in at least one region of the pipewall.

According to a fourth aspect of the present invention there is provideda method of manufacturing a pipe, comprising:

forming a pipe wall with a composite material comprising a matrix and aplurality of reinforcing fibres embedded within the matrix; and

establishing a varying level of pre-stress in the composite materialbetween different regions of the pipe wall.

The method may comprise forming a pipe in accordance with the thirdaspect. Features defined above in relation to the third aspect may alsobe associated with the fourth aspect.

According to a fifth aspect of the present invention there is provided apipe having a pipe wall comprising a composite material formed of atleast a matrix and a plurality of reinforcing fibres embedded within thematrix, wherein the modulus of the composite material varies throughoutthe pipe wall.

The modulus of the composite material may be varied by varying themodulus of the matrix, for example by varying the type of matrixmaterial. The modulus of the composite material may be varied by varyingthe modulus of one or more reinforcing fibres, for example by varyingthe type of reinforcing fibre.

The modulus of the composite material may be varied by varying thealignment angle of the reinforcing fibres. The fibre alignment angle maybe defined relative to the longitudinal axis of the pipe. For example, afibre provided at a 0 degree alignment angle will run entirelylongitudinally of the pipe, and a fibre provided at a 90 degreealignment angle will run entirely circumferentially of the pipe, withfibres at intermediate fibre alignment angles running bothcircumferentially and longitudinally of the pipe, for example in aspiral pattern.

The modulus of the composite material may be varied in a radialdirection within the pipe wall.

In one arrangement one or more fibres located within an outer region ofthe pipe wall may define a greater fibre alignment angle than one ormore fibres located within an inner region of the pipe wall. Forexample, one or more fibres in an outer region of the pipe wall maydefine a fibre alignment angle in the region of 75 to 90 degrees, andone or more fibres in an inner region of the pipe wall may define afibre alignment angle in the region of 65 to 80 degrees. In such anembodiment the inner fibres aligned at a lower alignment angle may becapable of accommodating higher hoop strains than the outer fibresaligned at a greater alignment angle. Such an arrangement may beadvantageous in conditions where internal and/or external pressures aredominant.

In an alternative arrangement one or more fibres located within an innerregion of the pipe wall may define a greater fibre alignment angle thanone or more fibres located within an outer region of the pipe wall. Suchan arrangement may be advantageous in combined load conditions, axialloading, bending moments, pressure loading or the like.

A radially inner region of the pipe wall may define a uniform modulus,and a radially outer region of the pipe wall may define a varyingmodulus. That is, the radially outer region may comprise at least twosections having different moduli. This arrangement may be achievedduring manufacture of the pipe by providing a pre-formed pipe structureor mandrel of uniform modulus and which defines the radially innerregion of the pipe wall, and then forming the radially outer pipe wallregion on the pre-formed mandrel, while including a variation in modulusin the radially outer region.

According to a sixth aspect of the present invention there is provided amethod of manufacturing a pipe, comprising:

forming a pipe wall with a composite material comprising a matrix and aplurality of reinforcing fibres embedded within the matrix; and

varying the modulus of the composite material throughout the pipe wall.

A pipe having a pipe wall may comprise a pipe having a pipe wallcomprising a composite material formed of at least a matrix and aplurality of reinforcing fibres embedded within the matrix, wherein atleast one longitudinal portion of the pipe wall comprises or defines alocal variation in construction to provide a variation in a property ofthe pipe.

According to a seventh aspect of the present invention there is provideda pipe having a pipe wall comprising a composite material formed of atleast a matrix and a plurality of reinforcing fibres embedded within thematrix, wherein the pipe wall comprises a local variation inconstruction in at least one longitudinal section such that the fibreconstruction in one longitudinal section of the pipe wall is differentfrom the fibre construction of the composite material in a differentlongitudinal section.

Thus, the pipe comprises a variation in construction of the compositematerial along the length of the pipe. Such an arrangement mayadvantageously permit the pipe to be optimised, along its length, for aparticular service condition, for example.

The variation in construction between the different longitudinalsections may be located at a common radial location within the pipewall. Such a common radial location may be determined from a commondatum point or surface, such as from an internal or external surface ofthe pipe.

The local variation in construction may be provided between at least twolongitudinal sections on a common circumferential plane within the pipewall.

The local constructional variation may be such that one longitudinalportion defines a different overall construction to that in a differentlongitudinal portion. In such an arrangement the pipe wall may compriseat least two longitudinal portions having different constructionalproperties.

Thus, the construction of the pipe wall includes one or more localvariations along its length to achieve a variation in a property of thepipe. That is, the constructional variation is sufficient to affect avariation in a property of the pipe.

In use, the local variation in a property of the pipe by virtue of thelocal constructional variation may establish a preferentialcharacteristic in the pipe. Such a preferential characteristic maybeneficially differ from that in a pipe of uniform construction alongits length, such as is known in the prior art. A preferential mechanicalcharacteristic may be achieved, such as a strength, stiffness, flexuralrigidity, bending, resonant characteristic, deformation characteristics,failure characteristics or the like. A preferential thermalcharacteristic may be achieved, such as a thermal expansioncharacteristic, thermal insulation characteristic or the like.

In embodiments of the present invention the preferential characteristicmay be provided to more closely match the properties of the pipe to adesired service condition or environment. For example, in serviceconditions in which environmental effects differ over the length of thepipe, such as may be the case with a pipe extending through variablewater depths, the provision of a longitudinal variation may permit thepipe to be more customised to the differing environmental properties.This may permit a reduction in material usage, costs, weight and thelike. That is, conventional pipes are globally designed to accommodatethe most extreme environmental conditions. However, the presentinvention permits variability to be incorporated within a pipe to permitcustomisation along its length.

The local constructional variation of the pipe wall may be configured tofocus a particular behavioural characteristic at one or morelongitudinal portions. This may permit a preferential control over thebehaviour of the pipe to be achieved, which may assist when in a servicecondition, storage configuration, deployment/retrieval configuration orthe like. For example, the local constructional variation may permit acontrolled deformation to be achieved within a longitudinal portion ofthe pipe, and in some embodiments to be substantially restricted to saidlongitudinal portion. Such deformation may include buckling,longitudinal expansion and contraction, radial expansion andcontraction, torsional deformation, bending or the like. Suchdeformation may include catastrophic failure, such as axial tensilefailure, hoop tensile failure or the like. For example, a localconstructional variation within the pipe may provide a portion ofreduced strength, such as reduced tensile strength, reduced hoopstrength or the like, which may focus any failure to occur within saidlongitudinal portion. In such an arrangement the specific longitudinalportion with reduced strength may be selected for ease of access,inspection, repair or the like. For example, in embodiments where thepipe is used in varying water depths, such as when used as a riser, forexample a vertical riser, catenary riser or the like, a longitudinalportion of the pipe in proximity of the surface may comprise a localconstructional variation to provide a region of minimum strength.

In some embodiments focusing a particular behavioural characteristic ata longitudinal portion of the pipe wall may permit multiple pipesaccording to the present aspect of the invention to be arranged inproximity to each other, wherein the local constructional variation ineach pipe facilitates a desired behavioural characteristic, such ascontrolled longitudinal bending, at a common location. This may preventor substantially minimise interference between the pipes, facilitatemore compact installations and the like. This arrangement may be ofapplication where, for example, multiple pipes are bundled in a commonlocation, extend along a common path or course, converge to a commonrestricted location from various directions or the like, such asconvergence towards a common floating vessel, for example a FPSO vesselused in the oil and gas industry.

At least one longitudinal portion may comprise a local variation inmodulus of elasticity. At least one longitudinal portion may comprise alocal variation in second moment of area. At least one longitudinalportion may comprise a local variation in coefficient of thermalexpansion. At least one longitudinal portion may comprise a localvariation in thermal conductivity. At least one longitudinal portion maycomprise a local variation in a material strength, such as a yieldstrength of a particular component of the composite material. At leastone longitudinal portion may comprise a local variation in tensilestrength. At least one longitudinal portion may comprise a localvariation in hoop strength. At least one longitudinal portion maycomprise a local variation in compressive strength. At least onelongitudinal portion may comprise a local variation in flexuralstrength. At least one longitudinal portion may comprise a localvariation in geometry, such as wall thickness.

A local constructional variation may be provided in a plurality oflongitudinal portions along the length of the pipe. For example alongthe complete length of the pipe.

The local constructional variation may define a discrete constructionalvariation in one longitudinal portion with respect to an adjacentlongitudinal portion. For example, the local constructional variationmay be provided in a step-wise or abrupt manner with respect to anadjacent portion.

The local constructional variation may comprise a tapered or gradualvariation, for example with respect to an adjacent region. A gradualvariation may be provided in one or more discrete longitudinal portionsof the pipe. Alternatively, a gradual variation may be provided over thecomplete length of the pipe.

The local constructional variation may comprise a constructionalvariation in the matrix of the composite material such that matrixconstruction in one longitudinal section of the pipe wall is differentfrom the matrix construction of the composite material in a differentlongitudinal section.

At least one longitudinal portion may comprise a local variation in thetype of matrix material. At least one longitudinal portion may comprisea local variation in the volume of matrix material.

At least one longitudinal portion may comprise a local variation in thedistribution density of the reinforcing fibres within the matrixmaterial. For example, the reinforcing fibres may be more densely packedtogether in one longitudinal portion of the pipe wall than anotherlongitudinal portion. In such an arrangement the region of increasedfibre packing density may define a region of modified stiffness, such asincreased stiffness, modified strength such as hoop strength, tensilestrength or the like.

At least one longitudinal portion may comprise a local variation in thetype of fibre within the composite material. That is, one longitudinalportion of the pipe wall may comprise a fibre type which is not presentin another longitudinal portion, or at least present in a differentquantity or configuration. At least one longitudinal portion maycomprise one or more fibres with a modified, such as increased ordecreased, stiffness, tensile strength or the like. At least onelongitudinal portion may comprise one or more reinforcing fibres with amodified dimension, such as a modified diameter. For example, onelongitudinal portion of the pipe wall may comprise fibres having adifferent diameter to those in a different longitudinal portion.

At least one longitudinal portion may comprise a local variation infibre alignment angle within the composite material. For example, one ormore reinforcing fibres in one longitudinal portion may define adifferent alignment angle to one or more reinforcing fibres in adifferent longitudinal portion, and/or one longitudinal portion maycomprise a different proportion or quantity of fibres which definesubstantially the same alignment angle as those in another longitudinalportion. In this arrangement the fibre alignment angle may be definedrelative to the longitudinal axis of the pipe. For example, a fibreprovided at a 0 degree alignment angle will run entirely longitudinallyof the pipe, and a fibre provided at a 90 degree alignment angle willrun entirely circumferentially of the pipe, with fibres at intermediatefibre alignment angles running both circumferentially and longitudinallyof the pipe, for example in a spiral pattern.

At least one longitudinal portion of the pipe wall may comprise a localvariation in fibre pre-stress. In this arrangement the fibre pre-stressmay be considered to be a pre-stress, such as a tensile pre-stressand/or compressive pre-stress applied to a fibre during manufacture ofthe pipe, and which pre-stress is at least partially or residuallyretained within the manufactured pipe. In this arrangement the fibrepre-stress in one longitudinal portion of the pipe wall may differ fromthat in a different longitudinal portion. In one arrangement the fibrepre-stress, such as pre-tension, in at least one longitudinal portion ofthe pipe wall may be increased relative to a different longitudinalportion. A local variation in fibre pre-stress may permit a desiredcharacteristic of the pipe to be achieved, such as a desired bendingcharacteristic. This may assist to position or manipulate the pipe, forexample during installation, retrieval, coiling or the like. Further,this local variation in fibre pre-stress may assist to shift a neutralposition of strain within the pipe wall, which may assist to providemore level strain distribution when the pipe is in use, and/or forexample is stored, such as in a coiled configuration.

At least one longitudinal portion of the pipe wall may comprise a localvariation in construction by use of at least one insert. The insert maybe considered to be a separate component from the matrix and reinforcingfibres which form the composite material of the pipe wall. The insertmay be formed separately and subsequently installed within at least onelongitudinal portion of the pipe wall. An insert may be installed withinthe pipe wall during manufacture of the pipe. An insert may be installedwithin the pipe wall following manufacture of the pipe.

The insert may define a structural insert. The insert may exhibitsufficient mechanical properties, such as stiffness, strength or thelike, to provide a measurable effect on the mechanical properties of theentire pipe. For example, a single strand of a reinforcing fibre may notfunction as an insert due to the magnitude of difference between thestructural properties of a single strand and the entire pipe. At leastone insert may comprise an elongate insert. At least one insert mayextend substantially longitudinally of the pipe. At least one insert maycomprise a plate, rod, cylinder pin or the like. At least one insert maycomprise a mesh structure or the like. At least one insert may comprisea metallic material, such as a metal alloy. At least one insert maycomprise a shape memory metal alloy. At least one insert may comprise anon-metallic material. At least one insert may comprise a compositematerial, such as a composite of a matrix with embedded reinforcingfibres. In this arrangement a composite insert may be formed separatelyand subsequently installed or included in at least one circumferentialsegment of the pipe wall.

The local constructional variation in the pipe wall may be selected toprovide a desired longitudinal bending characteristic along the pipe.Such a desired longitudinal bending characteristic may be achieved byproviding a local variation in stiffness within at least onelongitudinal portion of the pipe. A modified stiffness may be achievedby, for example, modifying the modulus of the composite material, forexample the matrix and/or the fibres, modifying the second moment ofarea, for example by providing more or less of the composite material,or the like. Such a local variation in stiffness may comprise areduction in stiffness. This may permit or bias bending to occur at thelongitudinal portion of the pipe comprising the reduced stiffness. Sucha local variation in stiffness may comprise an increase in stiffness.This may minimise the level of permitted bending at this specificlongitudinal portion. Such an increase in stiffness may be utilised inregions where loading or bending moments might be expected to be higher,for example at connections within other equipment, such as floatingvessels, well head equipment or the like.

The local constructional variation in the pipe wall may be selected toprovide a desired thermal expansion characteristic of the pipe. Forexample, a local constructional variation may be selected to permit thepipe to deform in a repeatable and expected manner upon thermalexpansion thereof. This may, for example, permit controlled buckling,lateral deflection or the like of the pipe to be achieved during thermalexpansion.

The local constructional variation in the pipe wall may be selected toprovide a desired thermal insulation characteristic of the pipe. Forexample, a variation in thermal conductivity within a longitudinalportion of the pipe wall may permit a desired thermal insulationproperty to be achieved within said portion. This may be advantageous incircumstances where different longitudinal portions of the pipe areexposed to different conditions when in use. For example, in oneembodiment a portion of the pipe may be buried, for example in a seabed,and a portion may be exposed to an ambient environment, such as the sea.In such an exemplary arrangement the longitudinal portion of the pipewhich is exposed to the ambient environment may be locally modified toexhibit greater thermal insulation properties that that portion which isburied. This may permit the pipe to be more accurately formed for itsintended use.

The local constructional variation in pipe wall may be selected toaccommodate or absorb an anticipated movement, deformation or the likewithin the pipe, such as a longitudinal expansion movement ordeformation. In such an arrangement the local constructional variationmay be selected to provide a desired compression property orcharacteristic to permit axial expansion of the pipe to be accommodatedwithin the associated longitudinal portion without any, or at leastwithout any significant lateral deflection or deformation.

The local constructional variation in the pipe wall may be selected toprovide a desired energy absorption characteristic of the pipe. Forexample, a local constructional variation may permit mechanical forcesto be absorbed in the at least one longitudinal portion. In such anarrangement a longitudinal portion of the pipe may function as a damper.A constructional variation may permit vibration forces to be absorbed inthe at least one longitudinal portion.

The local constructional variation in the pipe wall may be selected toprovide a desired acoustic characteristic of the pipe. For example, thelocal variation may permit the pipe to permit the transmission ofacoustic energy at the associated longitudinal portion. This may permitacoustic devices, such as transducers, to use the pipe wall at theassociated longitudinal portion to couple acoustic energy into/frommaterial contained therein. The local constructional variation may beselected to match the acoustic impedance of the pipe wall at theassociated longitudinal portion with a material contained, or expectedto be contained within the pipe. Such variations in acoustic propertiesmay permit acoustic measurements to be made, such as may be made duringflow metering measurements, fiscal monitoring or the like.

The local constructional variation in the pipe wall may be selected toprovide a desired resonant characteristic of the pipe. For example, atleast one longitudinal portion of the pipe may comprise a localvariation configured to provide a desired resonant mode of vibration.This arrangement may permit vortex induced vibrations to be reduced orminimised within or on the pipe when exposed to an external flowingfluid which has a lateral component relative to the pipe. Specifically,the present invention may permit at least one longitudinal portion ofthe pipe to provide a resonant mode of vibration which differs from avortex shedding frequency associated with the pipe and an anticipatedservice external flow condition.

The pipe may comprise or be associated with a measuring device locatedat one longitudinal portion of the pipe wall which comprises a localconstructional variation. In this arrangement the local constructionalvariation may facilitate improved measurement. For example, the localconstructional variation may be selected to permit focussing orexaggeration of movement in the longitudinal portion associated with themeasuring device.

The pipe may comprise or define a continuous pipe wall. Accordingly, theconstructional variation may not be provided by connecting two separatepipe sections together, and instead is provided by a local variation inconstruction within a single and continuous pipe wall.

The matrix of the composite material may define a continuous structure,wherein the reinforcing fibres are embedded within said continuousstructure. In this arrangement the composite material may effectively beprovided as a single layer throughout the thickness of the pipe wall,without any interfaces, such as bonded interfaces, between individuallayers.

The distribution of the reinforcing fibres may vary throughout thecontinuous matrix in a radial direction through the pipe wall. Thedistribution of the reinforcing fibres may vary from zero at the regionof the inner surface of the pipe wall, and be increased in a directiontowards the outer wall. Accordingly, the region of the inner surface ofthe pipe wall will be absent of reinforcing fibres.

The matrix of the composite material may continuously extend between twolongitudinal portions having variations in construction.

Continuous reinforcing fibres may extend between different longitudinalportions or regions of the pipe wall.

A radially inner region of the pipe wall may define a uniformconstruction along its length, and a radially outer region of the pipewall may define a varying construction between different longitudinalportions. That is, the radially outer region may comprise at least twosections having different constructions. This arrangement may beachieved during manufacture of the pipe by providing a pre-formed pipestructure or mandrel of uniform longitudinal construction and whichdefines the radially inner region of the pipe wall, and then forming theradially outer pipe wall region on the pre-formed mandrel, whileincluding a variation in construction between two different longitudinalregions.

A method of manufacturing a pipe may comprise:

forming a pipe wall with a composite material comprising a matrix and aplurality of reinforcing fibres embedded within the matrix; and

creating a local variation in the construction of the pipe wall withinat least one longitudinal portion of the pipe wall to provide avariation in a property of the pipe.

According to a eighth aspect of the present invention there is provideda method of manufacturing a pipe, comprising:

forming a pipe wall with a composite material comprising a matrix and aplurality of reinforcing fibres embedded within the matrix; and

varying the fibre construction of the composite material in at least onelongitudinal portion of the pipe wall such that the fibre constructionin one longitudinal portion differs from the fibre construction in adifferent longitudinal portion.

The method may comprise forming a pipe in accordance with any otheraspect. Features defined above in relation to any other aspect may alsobe associated with the present aspect.

A pipe having a pipe wall may comprise a composite material formed of atleast a matrix and a plurality of reinforcing fibres embedded within thematrix, wherein the matrix defines a continuous structure and the fibresare variably distributed within the continuous matrix structure.

According to a ninth aspect of the present invention there is provided apipe having a pipe wall comprising a composite material formed of atleast a matrix and a plurality of reinforcing fibres embedded within thematrix, wherein the matrix defines a continuous structure and the fibresare variably distributed radially throughout the continuous matrix fromzero at the region of the inner surface of the pipe wall, and beincreased in a direction towards the outer wall.

Accordingly, the region of the inner surface of the pipe wall will beabsent of reinforcing fibres.

In this arrangement the composite material may effectively be providedas a single layer throughout the thickness of the pipe wall, without anyinterfaces, such as bonded interfaces, between individual layers.

The matrix may define a continuous structure between inner and outersurfaces of the pipe wall.

A method of manufacturing a pipe may comprise forming a pipe wall with acontinuous matrix material and variably distributing reinforcing fibresthroughout the matrix material.

According to a tenth aspect of the present invention there is provided amethod of manufacturing a pipe, comprising forming a pipe wall with acontinuous matrix material and variably distributing reinforcing fibresradially throughout the continuous matrix from zero at the region of theinner surface of the pipe wall and increasing in a direction towards theouter wall.

According to an eleventh aspect of the present invention there isprovided a pipe system, comprising:

a first pipe section having a wall comprising a metal material; and

a second pipe section coupled to the first pipe section in end-to-endrelation and having a wall comprising a composite material formed of atleast a matrix and a plurality of reinforcing fibres embedded within thematrix,

wherein the second pipe section is configured to sustain a greater levelof strain than the first pipe section when the pipe system is subject todeformation by a load event.

The second pipe section may comprise a pipe according to any otheraspect.

Accordingly, during deformation of the pipe system caused by a loadevent, a greater proportion of strain will be sustained by the secondpipe section. This may assist in minimising the level of strain appliedwithin the first pipe section, to the extent that a greater proportionof the strain induced within the pipe system during a load event will besustained within the second pipe section. As such, the second pipesection may function to protect the first pipe section during adeformation and load event applied to the pipe system. For example, thesecond pipe section may be configured to prevent or substantiallyminimise the risk of strains and/or stresses being applied within thefirst pipe section which may cause yield limits of the metal material ofsaid first pipe section to be exceeded. The second pipe section may beconfigured to minimise the risk of failure, material fatigue, adverse orundesired elastic or plastic deformation, or the like, of the first pipesection.

The pipe system may be configured such that a larger proportion ofdeformation within said system caused by a load event is focussed withinthe second pipe section. Accordingly, the second pipe section may beconfigured to accommodate a relatively greater proportion of deformationthan the first pipe section. In embodiments of the present invention thesecond pipe section is configured to accommodate or absorb substantiallyall deformation of the pipe system during a load event.

The second pipe section may be configured to sustain a greater level ofstrain than the first pipe section when the pipe system is subject todeformation by a cyclical load event. Such a cyclical load event may beestablished during intermittent flow through the pipe system, duringmulti phase flow through the pipe system, during vortex shedding eventswhen the pipe system is immersed in a flowing fluid, or the like.

The second pipe section may be configured to sustain a greater level ofstrain than the first pipe section when the pipe system is subject todeformation by an applied axial load. Accordingly, in this arrangementthe second pipe section may be configured to accommodate a largerrelative degree of axial expansion and/or contraction. In embodiments ofthe present invention, where an axial load is applied to the pipe systemsubstantially all resulting axial deformation is absorbed by orrestricted to the second pipe section.

The second pipe section may be configured to sustain a greater level ofstrain than the first pipe section when the pipe system is subject todeformation by an applied radial load.

The second pipe section may be configured to sustain a greater level ofstrain than the first pipe section when the pipe system is subject todeformation by a bending moment. Accordingly, in this arrangement thesecond pipe section may be configured to accommodate a larger relativedegree of longitudinal bending. In embodiments of the present invention,where a bending moment is applied to the pipe system substantially alllongitudinal bending is absorbed by or restricted to the second pipesection.

The second pipe section may be configured to sustain a greater level ofstrain than the first pipe section when the pipe system is subject todeformation by an applied torsional load. Accordingly, in thisarrangement the second pipe section may be configured to accommodate alarger relative degree of twisting. In embodiments of the presentinvention, where a torsional load is applied to the pipe systemsubstantially all resulting twisting deformation is absorbed by orrestricted to the second pipe section.

A load event may be considered to be any event which applies a load orstress to or within the pipe system.

In one embodiment a load event may be established by thermal propertiesof the pipe system, for example thermal properties of one or both of thefirst and second pipe sections. A load event may be established bythermal expansion and/or contraction of the pipe system. In such anarrangement, deformation caused by thermal expansion and/or contractionmay be accommodated, for example substantially entirely accommodated, bythe second pipe section. For example, thermal expansion of one or bothof the first and second pipe sections may generate a compressive axialload or stress within the pipe system. In such an arrangement oreventuality the second pipe section may be configured to sustain agreater level of compressive strain than the first pipe section.Further, thermal contraction of one or both of the first and second pipesections may generate a tensile axial load or stress within the pipesystem. In this arrangement or eventuality the second pipe section maybe configured to sustain a greater level of tensile strain than thefirst pipe section.

A load event may be established by exposure of the pipe system to aservice environment. For example external equipment or the like mayengage the pipe system to generate an applied load. Further, anenvironmental condition may establish an applied load, such as internalor external fluid pressure, for example during submergence of the pipesystem, fluid drag, vortex induced vibration, for example duringsubmergence in a flowing fluid, or the like.

The second pipe section may define a greater resistance to one or morefailure modes under load than the first pipe section. For example, thesecond pipe section may define a greater resistance to a bucklingfailure mode than the first pipe section. In such an arrangement thesecond pipe section may be configured to accommodate a greater degree ofaxial compressive loading or stress than the first pipe section prior toa buckling event. The second pipe section may be configured toaccommodate a greater degree of axial compressive strain than the firstpipe section prior to a buckling event. Accordingly, the second pipesection may sustain a greater level of strain than the first pipesection while retaining a substantially straight configuration.

The second pipe section may define a greater resistance to a tensilefailure mode than the first pipe section.

The composite material of the second pipe section may be constructed topermit said pipe section to sustain a greater level of strain than thefirst pipe section when the pipe system is subject to deformation by anapplied load. For example, the composite material may comprisesdesirable constructional properties, such as matrix type, fibre type,fibre alignment angle, composite material pre-stress, fibre packingdensity or the like.

The second pipe section may define a substantially straight pipesection. The substantially straight second pipe section may beconfigured to remain substantially straight during deformation of thepipe system caused by an axial load.

The second pipe section may be configured to be deformed laterallyduring deformation of the pipe system caused by an axial load. In suchan arrangement deformation of the pipe system may be accommodated in acontrolled manner by lateral deflection of the second pipe section.

The second pipe section may define a bent pipe section, wherein saidbent pipe section may be configured to absorb deformation within thepipe system caused by an applied load. In such an arrangement, thecomposite material of the second pipe section may permit effects ofcyclical loading to be minimised. For example, material fatigue is notof particular concern in composite material.

According to a twelfth aspect of the present invention there is provideda pipe system comprising:

a first pipe section having a wall comprising a metal material; and

a second pipe section provided in accordance with any other aspect,wherein the second pipe section provides a local variation in a propertyof the pipe system along the length of the pipe system.

According to a thirteenth aspect of the present invention there isprovided a method of manufacturing a pipe system, comprising:

providing a first pipe section having a wall comprising a metalmaterial; and

coupling a second pipe section in accordance with any other aspect to anend of the first pipe section, wherein the second pipe section providesa local variation in a property of the pipe system along the length ofthe pipe system.

According to a fourteenth aspect of the present invention there isprovided a pipe having a pipe wall comprising a composite materialformed of at least a matrix and a plurality of reinforcing fibresembedded within the matrix, wherein the construction of the compositematerial within the pipe wall is varied along the length of the pipe.

According to a fifteenth aspect of the present invention there isprovided a pipeline or pipe system comprising:

a metallic pipe section having a wall comprising a metallic material;and

a deformation absorber coupled to the metallic pipe section andcomprising a composite pipe section having a wall comprising a compositematerial formed of at least a matrix and a plurality of reinforcingfibres embedded within the matrix, wherein the composite material isconstructed to cause the deformation absorber to sustain a greater levelof strain than the metallic pipe section when the pipeline is subject todeformation by a load event such that a larger proportion of deformationwithin the pipeline caused by a load event is focussed within thedeformation absorber.

According to a sixteenth aspect of the present invention there isprovided a pipe having a pipe wall comprising a composite materialformed of at least a matrix and a plurality of reinforcing fibresembedded within the matrix, wherein a radially inner region of the pipewall is of uniform construction and an outer region of the pipe wall isof varying construction.

The variation in construction in the outer region may comprise avariation in construction between different geometric portions of theouter region, such that the construction in one geometric portiondiffers from the construction in a different geometric portion. Thevariation in construction in the outer region may comprise a variationbetween different longitudinal portions, different radial portionsand/or different circumferential portions.

The variation in construction may comprise or be defined by anyvariation in construction defined in relation to any other aspect.

The pipe may be manufactured by providing a pre-formed pipe structure ormandrel of uniform construction and which defines the radially innerregion of the pipe wall, and then forming the radially outer pipe wallregion on the pre-formed mandrel, while including one or more variationsin construction therein.

According to a seventeenth aspect of the present invention there isprovided a method of manufacturing a pipe having a pipe wall comprisinga composite material formed of at least a matrix and a plurality ofreinforcing fibres embedded within the matrix, the method comprising:

providing a pre-formed pipe structure or mandrel of uniform constructionto define the radially inner region of a pipe wall; and

forming a radially outer pipe wall region on the pre-formed mandrel,while including one or more variations in construction therein.

The pre-formed pipe structure may comprise both matrix and fibres. Thepre-formed pipe structure may be free from fibres.

In one or more of the aspects defined above the matrix material maycomprise a polymer. The matrix material may comprise a thermoplasticcomponent. The matrix material may comprise a thermoset component. Thematrix material may comprise a polyaryl ether ketone, a polyaryl ketone,a polyether ketone, a polyether ether ketone, a polycarbonate or thelike, or any suitable combination thereof. The matrix material maycomprise a resin, such as an epoxy resin or the like.

The reinforcing fibres may comprise continuous or elongate fibres. Thereinforcing fibres may comprise any one or combination of carbon, glass,polymer, basalt, aramid fibres or the like. The reinforcing fibres maycomprise discontinuous fibres.

In some embodiments the composite material may comprise a matrix andfibres formed of similar or identical materials. For example, acomposite material may comprise one or more reinforcing fibres which areformed of the same material as the matrix, albeit in a fibrous, drawn,elongate form or the like.

In one or more of the aspects defined above the defined pipe may beconfigured for use above the ground. The pipe may be configured for useat least partially buried. The pipe may be configured for use in asubterranean environment. The pipe may be configured for use in a subsealocation.

The pipe of any aspect may be rigid or quasi or substantially rigid. Thepipe may be configured to define a minimum bending radius of at least 50diameters. In some embodiments the pipe may be configured to define aminimum bend radius of at least 5 diameters, for example between 5 to 10diameters.

The pipe may be configured for use as part of, for example, a riser,such as a vertical riser, catenary riser or the like, a flow line, ajumper or the like, or any combination thereof. The pipe may beconfigured for use in transporting a fluid, providing a confined conduitfor tooling or the like, such as may be used in subterranean wellboredrilling operations, completion operations, intervention operations andthe like.

The pipe may be configured for use in transporting product associatedwith the extraction of hydrocarbons from subsea reservoirs, includingaccommodating the flow of hydrocarbons, carbon dioxide, water, otherchemicals, solid matter, fluid and gas mixes and the like.

The pipe may be configured for use in carbon dioxide or other gassequestration.

The pipe in any aspect may define an oilfield pipe or tubular. Such anoilfield pipe or tubular may be one which is used for the conveyance ofany fluid or any material or equipment associated with in theexploration, extraction, processing and transporting of hydrocarbonproduct.

Further aspects of the present invention may relate to methods ofdeploying and/or retrieving a pipe to/from a spool, such as a pipeaccording to any other aspect.

Further aspects of the present invention may relate to a pipe systemcomprising multiple pipes according to one or more previous aspects,which may be formed, for example by the incorporation of localconstructional variations in the composite material, to accommodateproximity to each other.

Principles of the present invention defined in one or more of theaspects presented above may be applied to elongate solid bodies. Thatis, principles of the present invention defined in one or more of theaspects presented above may be applied to elongate bodies which do notinclude an internal bore. In such an arrangement the elongate body maydefine composite wireline, slickline or the like.

It should be understood that the features defined above in accordancewith any aspect of the present invention may be utilised, either aloneor in combination with any other defined feature, in any other aspect ofthe invention.

For example, an aspect of the present invention may relate to a pipehaving a pipe wall comprising a composite material formed of at least amatrix and a plurality of reinforcing fibres embedded within the matrix,wherein the pipe wall comprises or defines at least one of:

a local constructional variation in at least one circumferential segmentof the pipe wall;

pre-stress in at least one region of the pipe wall and

a local constructional variation in at least one longitudinal portion ofthe pipe wall

It should be understood that although terms such as “circumferential”and “radial” are used herein, these and similar terms are not intendedto limit the pipe to being circular in cross-section. Instead, the pipemay be of any cross-sectional shape, such as oval, rectilinear or thelike, and a circumferential segment may be considered to be a segment orsector of a perimeter of the pipe.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention will now be described,by way of example only, with reference to the accompanying drawings, inwhich:

FIG. 1 is a lateral cross-sectional view of a pipe in accordance with anembodiment of one or more aspects the present invention;

FIG. 2 is a side view of the pipe of FIG. 1, shown in a curved or bentconfiguration;

FIG. 3 is a diagrammatic illustration of a pipe in accordance with analternative embodiment of one or more aspects of the present invention;

FIG. 4 is a lateral cross-sectional view of a composite pipedemonstrating a composition of a matrix material and embeddedreinforcing fibres which forms the pipe wall;

FIG. 5 is a diagrammatic illustration of a composite pipe in accordancewith an embodiment of one or more aspects of the present invention;

FIG. 6 is a diagrammatic illustration of a composite pipe in accordancewith an alternative embodiment of one or more aspects of the presentinvention;

FIG. 7 is a diagrammatic illustration of a composite pipe in accordancewith another alternative embodiment of one or more aspects the presentinvention;

FIG. 8 is a diagrammatic illustration of a pipe in accordance with afurther alternative embodiment of one or more aspects the presentinvention;

FIG. 9 is a diagrammatic illustration of a pipe in accordance with ageneral embodiment of one or more aspects of the present invention,wherein the pipe includes a local constructional variation in alongitudinal portion thereof;

FIG. 10 is a diagrammatic illustration of a pipe used as a verticalriser in accordance with an embodiment of one or more aspects thepresent invention;

FIG. 11 is a diagrammatic illustration of a pipe used as a vertical risein accordance with an alternative embodiment of one or more aspects thepresent invention;

FIG. 12 is a diagrammatic illustration of a pipe used as a catenary typeriser in accordance with an embodiment of one or more aspects of thepresent invention;

FIGS. 13A and 13B illustrate a variation in bending moment applied to apipe, and also a pipe embodiment formed according to one or more aspectsof the present which accommodates the variation in bending moment;

FIG. 14 illustrates a pipe according to a further embodiment of one ormore aspects the present invention, wherein the pipe includes alongitudinal portion configured to focus longitudinal bending withinsaid portion;

FIG. 15 illustrates an embodiment of a pipe system which includes aplurality of pipes according to one or more aspects of the presentinvention, wherein the pipes are shown converging on a common location;

FIG. 16 illustrates an alternative embodiment of a pipe system whichincludes a plurality of pipes according to one or more aspects of thepresent invention, wherein the pipes are each shown with a bend focussedat a common location;

FIGS. 17A and 17B illustrate a pipe according to another embodiment ofone or more aspects of the present invention, wherein the pipe includesa longitudinal portion configured to focus longitudinalexpansion/contraction within said portion;

FIG. 18 illustrates a pipe according to a further embodiment of one ormore aspects of the present invention, wherein the pipe includes alongitudinal portion configured to focus lateral buckling within saidportion;

FIG. 19 illustrates a pipe according to a still further embodiment ofone or more aspects of the present invention, wherein the pipe includesa longitudinal portion configured to focus radial expansion within saidportion;

FIG. 20 illustrates a pipe according to a still further embodiment ofone or more aspects of the present invention, wherein the pipe includesa longitudinal portion configured to focus tensile failure within saidportion;

FIG. 21 illustrates a pipe according to another embodiment of one ormore aspects of the present invention, wherein the pipe includes alongitudinal portion configured for accommodating a measurement device;

FIG. 22 is a diagrammatic side view of a pipe system in accordance withan embodiment of one or more aspects of the present invention;

FIGS. 23A and 23B are diagrammatic side views of a pipe system accordingto an embodiment of one or more aspects of the present invention,wherein the pipe system includes a composite pipe section configured tofocus longitudinal expansion/contraction within said composite section;

FIG. 24 is a diagrammatic side view of a further embodiment of one ormore aspects of the present invention, wherein the pipe system include acomposite pipe section configured to focus lateral buckling with saidsection; and

FIG. 25 is a lateral cross-sectional view of a pipe in accordance withan embodiment of one or more aspects the present invention.

DETAILED DESCRIPTION

A composite pipe, generally identified by reference numeral 10, inaccordance with an embodiment of the present invention is shown in FIG.1, wherein a lateral sectional view is provided to illustrate theexemplary structure of the pipe wall 12 across its thickness. The pipemay be suitable for use in a number of applications, such as in therecovery of hydrocarbons from a subterranean reservoir. For example, thepipe may be used as a riser, flow line, jumper, coiled tubing or thelike.

The pipe wall 12 comprises a composite material formed of a matrix and aplurality of reinforcing fibres embedded within the matrix. The matrixand reinforcing fibres are not individually illustrated in FIG. 1 forclarity. The matrix material may comprise a polymer, such as athermoplastic polymer, and in some embodiments the matrix may comprisepolyether ether ketone (PEEK). The reinforcing fibres may comprisecarbon fibres, glass fibres or the like.

In the embodiment shown the pipe wall 12 has a generally global andconsistent construction provided by the composite material of matrix andembedded fibres. Further, the matrix of the composite material in thepresent embodiment defines a continuous circumferential structure. Thatis, no discontinuities extending through the entire wall thickness arepresent. However, the pipe wall 12 defines two diametrically opposedcircumferential segments 14, 16 (identified in broken outline) which lieon the X-X plane and which each comprise a local variation inconstruction, identified by reference numerals 18 and 20. As will bedescribed in further detail below, the local constructional variations18, 20 in the respective segments 14, 16 are intended to provide localvariations in a property of the pipe.

Although a number of possible constructional variations according to thepresent invention may be possible, in the present embodiment a localvariation in fibre alignment angle is provided. Specifically, each localvariation 18, 20 within its respective segment 14, 16 comprises a localvariation in fibre alignment in which a number of fibres are arranged toextend longitudinally or axially of the pipe 10. More specifically, theindividual fibres within the local constructional variations 18, 20extend at 0 degrees relative to the central axis 22 of the pipe 10. Thisexemplary arrangement of each local variation 18, 20 has the effect ofproviding a local increase in axial stiffness within the segments 14,16. As the segments 14, 16 are diametrically opposed, the local increasein stiffness results in an increase in pipe stiffness in the X-X plane.Accordingly, bending of the pipe 10 in a longitudinal direction will beencouraged to occur along the X-X plane, which will thus define aneutral plane of bending. This preferential longitudinal bending isdemonstrated in FIG. 2. This ability to provide a repeatable bendingform of the pipe may provide significant advantages, for example interms of deployment, retrieval, commissioning, during use and the like.Such bending of the pipe 10 may occur in order to spool to pipe 10to/from a reel (not shown). Further, such bending may occur wheninstalling the pipe, for example to permit the pipe to be installed on aseabed from a floating vessel, to accommodate installation architectureand the like.

In the exemplary embodiment the upper and lower remaining segments 24,26 will thus define regions of lower stiffness which lie at a distancefrom the neutral X-X plane. Accordingly, the material within the upperand lower segments will carry a highest proportion of strain throughoutthe pipe wall 12, but will, nevertheless, be exposed to a reduced stresslevel due to the effect of the higher stiffness in the circumferentialsegments 14, 16. As such, the exemplary embodiment in FIG. 1 may permitsafety of the pipe to be increased, and permit a reduction in thepermissible bend radius or spool diameter to be achieved. Further, therequired material content may be reduced which may have an advantageouseffect on costs, weight etc.

In some embodiments the pipe 10 may include local variations in apretension applied within one or more reinforcing fibres within the pipewall. In one example a number of fibres within the lower segment 26 maybe provided within the matrix material at a higher tension than those inthe upper segment 24. This may have the additional effect of encouragingbending in the manner illustrated in FIG. 2.

In the embodiment described above the local variation 18, 20 in eachcircumferential segment 14, 16 may be provided along the entire lengthof the pipe 10, such that the entire pipe includes a local propertyvariation. However, in other examples only discrete longitudinalportions of the pipe 10 may include the local constructional variations18, 20. This may be of application in regions of a pipe 10 which mustincorporate a bend when installed. Furthermore, different longitudinalportions of the pipe 10 may include different constructional variationsin different circumferential segments.

In the embodiment shown in FIG. 1, each local constructional variation18, 20 is shown as being located within only a portion of the respectivesegments 14, 16, specifically intermediate the inner and outer walls 28,30. However, in other embodiments a local variation may extend to one orboth of the inner and outer walls 28, 30.

As described above, an exemplary embodiment of the present inventionincludes local variations in axial stiffness provided by a localvariation in fibre alignment. However, in other embodiments a stiffnessvariation may be achieved by use of a different type of fibre. Forexample, the pipe wall 12 may largely comprise T300 (230GPa) carbonfibre within the composite material, whereas the circumferentialsegments 14, 16 may comprise M40j (377GPa) carbon fibre. Further, thepipe wall 12 may largely comprise fibres of Eglass within the compositematerial, whereas the circumferential segments 14, 16 may comprise T300(230GPa) carbon fibre.

Further, a stiffness variation may be achieved by use of a differentdensity of fibres within segments 14, 16, use of a different matrixmaterial, variation in geometry, such as cross-sectional shape, wallthickness, or the like.

Also, each segment 14, 16 may be configured to define or comprise alocal variation in a property in addition to, or alternatively to,stiffness. For example, one or more segments may comprise a localvariation in a thermal coefficient, such as a coefficient of thermalexpansion. In such an alternative embodiment a segment with a differingcoefficient of thermal expansion may encourage a particular deformationof the pipe when thermal expansion occurs.

Furthermore, one or more circumferential segments within the pipe may beconfigured to comprise or define a local variation in strength. In onealternative or supplemental embodiment, one or more circumferentialsegments may comprise or define a local increase in tensile strength.Such a local increase in tensile strength throughout individual segmentsof the circumference of the pipe, as opposed to the entirecircumference, may permit the pipe to support a larger global tensionwhile permit a reduction in material usage, costs and the like.

As described above, in the embodiment shown in FIG. 1 each localconstructional variation 18, 20 is provided by a constructionalvariation in the composite material which forms the pipe wall 12.However, in other embodiments one or more constructional variations maybe provided by an insert, such as a metal insert, separate compositeinsert or the like.

An alternative embodiment of a pipe, generally identified by referencenumeral 50, is shown in FIG. 3, wherein the pipe 50 is shown in lateralcross-section and partially embedded within a seabed 52. In thisembodiment an upper circumferential segment 54 comprises a variation inconstruction, relative to a lower segment 56, which provides a localdecrease in thermal conductivity. As such, the portion of the pipe 50which will, in use, be exposed to a sea environment 60 will exhibit agreater degree of thermal insulation, which would not be required inthat portion of the pipe which is buried within the seabed 52. Thisparticular embodiment of the invention may also incorporatecircumferential segments which include local variations in stiffness,such as provided in the embodiment of FIG. 1, to ensure that theillustrated orientation of the pipe 50 is ensured during deployment andinstallation.

A lateral cross-sectional view of a pipe, generally identified byreference numeral 70, in accordance with an embodiment of the presentinvention is shown in FIG. 4. The pipe 70 comprises a pipe wall 72 whichis formed of a composite of a matrix material 74 and a plurality ofreinforcing fibres 76 embedded within the matrix 74. The matrix material74 defines a continuous structure, such that no interfaces, such asbonding interfaces, are presented throughout the radial extent of thepipe wall 72. This arrangement permits a more robust structure to beprovided, without risk of introducing internal weakness, stress raisersand the like by separate interface regions. Further, the elimination ofinterfaces within the pipe wall may minimise the risk of gas pocketsforming within the pipe wall at such interfaces, which may otherwiselead to adverse effects, for example during pressure cycles. The fibres76 are variably distributed throughout the pipe wall thickness betweenan inner pipe surface 78 and an outer pipe surface 80. The variabledistribution is such that no fibres 76 are provided in the regionadjacent the inner pipe surface 78. This arrangement may permit theinner surface region of the pipe 70 to remain entirely fluid tight,without any possible introduction of permeability by the presence offibres.

The arrangement shown in FIG. 4 may also incorporate one or more localconstructional variations, for example in one or more circumferentialsegments such as described above, and/or in one or more longitudinalportions such as defined later below, and/or with a varying degree ofpre-stress such as defined immediately below.

A composite pipe, generally identified by reference numeral 100, inaccordance with an embodiment of the present invention is shown in FIG.5, wherein a lateral sectional view is provided to illustrate theexemplary structure of the pipe wall 102 throughout its thickness. Thepipe 100 may be suitable for use in a number of applications, such as inthe recovery of hydrocarbons from a subterranean reservoir. For example,the pipe 100 may be used as a riser, flow line, jumper, coiled tubing orthe like, and may be locatable in a subsea location. As such, inembodiments of the present invention the pipe may be specificallydesigned to accommodate both internal and external pressures, as will bediscussed in more detail below.

The pipe wall 102 comprises a composite material formed of a matrix anda plurality of reinforcing fibres embedded within the matrix. The matrixand reinforcing fibres are not individually illustrated in FIG. 5 forclarity. The matrix material may comprise a polymer, such as athermoplastic polymer, and in some embodiments the matrix may comprisepolyether ether ketone (PEEK). The reinforcing fibres may comprisecarbon fibres, glass fibres or the like.

One principal feature of the present invention shown in the exemplaryembodiment of FIG. 5 is the application of a pre-stress within thecomposite material forming the pipe wall 102, and in the presentembodiment the pre-stress within the composite material is providedlargely by applying a pre-stress to the reinforcing fibres of thecomposite material during manufacture of the pipe. More specifically,the pipe wall 102 is formed using elongate reinforcing fibres within atape, rovings, tows or the like, wherein the tape, rovings, tows or thelike is/are manipulated, for example wound, to form the pipe wall 102,with pre-stress being applied within the fibres during thismanipulation. This pre-stress may be pre-tension and/or pre-compression.As will be described in detail below, the pre-stress within thecomposite material of the pipe wall 102 is provided to achieve a desiredstress and/or strain distribution within the pipe wall 102 when the pipe100 is exposed to an anticipated condition, such as an anticipatedservice condition.

In the embodiment shown in FIG. 5 the pipe wall 102 defines at least tworegions, specifically an inner region 104 and an outer region 106,wherein the outer region 106 entirely circumscribes the inner region104. A level of pre-tension is applied to the composite material withinthe outer region 106, as demonstrated by the enlarged view of a fibre108 which is shown to carry a tension t. In this embodiment thepre-tension t applied in the outer layer 106 is sufficient to establisha compressive hoop strain in the composite material within the innerregion 104, as demonstrated by the enlarged view of a fibre 110 which isshown under a compression C. Thus, the pipe wall 102 is formed to defineor comprise a varying pre-stress throughout the composite material,which has the effect of providing an even global stress and/or straindistribution within the pipe wall 102 when exposed to an anticipatedservice condition. Further, the variation in the level of pre-stressbetween the different regions 104, 106 permits a neutral position ofstrain within the pipe wall 102 to be desirably affected, for example toaccommodate a particular service condition or the like.

More specifically, the embodiment shown in FIG. 5 may be arranged foruse in a service condition in which the internal pipe pressure isdominant, that is, in a service condition in which the product of theinner pressure Pi and the inner radius Ri is greater than the product ofthe outer or external pressure Po and the outer radius Ro (i.e.,PiRi>PoRo). In such a service condition the composite material withinthe inner region 104 will typically be exposed to a greater tensilestrain than the composite material in the outer region 106. As such,with increasing load as a result of increasing internal pressure Pi, afailure strain level may be achieved first in the inner region 104.However, by provision of pre-tension t in the outer region 106 which hasthe effect of applying pre-compression C within the composite materialof the inner layer 104, the inner layer may be permitted or enabled tosupport a greater degree of strain before a failure strain limit isreached.

An alternative arrangement is shown in FIG. 6 which is configured foruse in a service condition in which external pressures are dominant(i.e., PiRi<PoRo) and the resultant hoop stresses will be compressive.The pipe shown in FIG. 6 is largely similar to that in FIG. 5 and assuch common reference numerals have been used. Accordingly, the pipe 100comprises a pipe wall 102 which includes inner and outer regions orlayers 104, 106. However, in the present embodiment in FIG. 6, thecomposite material of the inner layer 104 includes a greater pre-tensionthan the composite material in the outer layer 106. This is demonstratedby a fibre 110 of the inner layer 104 being under a pre-tension T whichis greater than a pre-tension t applied to a fibre 108 in the outerlayer 106 (i.e., T>t).

In alternative embodiments the effects of dominant internal and/orexternal pressures may be accommodated alternatively, or additionally,by providing a variation in the modulus of the composite materialthroughout the pipe wall. Such a variation in modulus may be achieved byvarying the matrix type, varying the fibre type, varying the fibrealignment angle or the like. The fibre alignment angle may be definedrelative to the longitudinal axis of the pipe. For example, a fibreprovided at a 0 degree alignment angle will run entirely longitudinallyof the pipe, and a fibre provided at a 90 degree alignment angle willrun entirely circumferentially of the pipe, with fibres at intermediatefibre alignment angles running both circumferentially and longitudinallyof the pipe, for example in a spiral pattern.

In one specific example, which may be adapted for service conditions inwhich internal pressures are dominant and as such is described againwith reference to FIG. 5, the fibres in the outer layer 106 define agreater alignment angle than those in the inner layer 104. For example,the fibres in the outer layer 106 may define a fibre angle in the regionof 85 degrees, and the fibres in the inner layer 104 may define a fibreangle in the region of 75 degrees. As such, the fibres in the innerlayer 104 may be capable of accommodating higher hoop strains.

In another specific example, the fibres in the outer layer 106 maydefine a lower alignment angle than those in the inner layer 104.

In other embodiments of the present invention a variation in pre-stress,and optionally also composite modulus, may be provided in otherdirections within the pipe other than radially.

For example, in the embodiment shown in FIG. 7 a pipe 120 comprises apipe wall 122 which is formed of a composite material which has ordefines a pre-stress which varies circumferentially of the pipe. Forexample, a level of pre-stress in one circumferential segment 124 of thepipe wall 122 differs from that in another circumferential segment 126.In the specific example shown fibres 128 in segment 124 are providedwith a greater pre-tension T than fibres 130 in segment 126 (i.e., T>t).This particular embodiment may permit a preferential bias to beintroduced into the pipe, such as permitting the pipe to preferentiallybend about horizontal plane X-X.

In a further example, as demonstrated in FIG. 8, a pipe 140 is formed ofa composite material which has or defines a pre-stress which varieslongitudinally of the pipe. For example, a level of pre-stress in onelongitudinal portion 144 of the pipe may differ from that in anotherlongitudinal portion 146. In the specific example shown fibres 148 inportion 144 are provided with a greater pre-tension T than fibres 150 inportion 146 (i.e., T>t). This particular embodiment may permit aparticular region of the pipe 140 to define higher hoop or burststrengths, for example. Further, this particular embodiment may permitlongitudinal bending, elongation, twisting or the like of the pipe 140to be focussed in a particular portion, such as in portion 146. Further,the longitudinal variation in pre-stress may be provided to create afocussed and specific weak point within the pipe. In such an arrangementif failure of the pipe might occur, such as due to extreme events, suchfailure may be restricted to a particular region, facilitating ease ofinspection, repair and the like.

The different pre-stress arrangements defined above, and their differentvariations, may be provided individually or with some in combination.

A generalised embodiment of a composite pipe is shown in FIG. 9, whereinthe pipe is identified by reference numeral 200. The pipe may besuitable for use in a number of applications, such as in the recovery ofhydrocarbons from a subterranean reservoir. For example, the pipe may beused as a riser, flow line, jumper, coiled tubing or the like.

The wall 202 of the pipe 200 comprises a composite material formed of amatrix and a plurality of reinforcing fibres embedded within the matrix.The matrix and reinforcing fibres are not individually illustrated inFIG. 9 for clarity. The matrix material may comprise a polymer, such asa thermoplastic polymer, and in some embodiments the matrix may comprisepolyether ether ketone (PEEK). The reinforcing fibres may comprisecarbon fibres, glass fibres or the like.

In the embodiment shown the pipe wall 202 comprises a longitudinalportion 204, delimited by broken outline, which comprises or defines alocal variation in the construction of the composite material. That is,the construction of the composite material in the longitudinal portion204 differs to that in a further longitudinal portion, such as adjacentlongitudinal portion 206. Although a step-wise variation between thelongitudinal portions 204, 206 is illustrated by the broken lines, inembodiments of the invention a tapering variation may be provided. Infact, in some embodiments, as will be described in further detail below,a tapering variation may be provided across the whole length of acomposite pipe.

Although discussed in further detail below, the local constructionalvariation in the longitudinal portion 204 is provided to establish avariation in a property within the pipe 200 which may in turn establisha preferential characteristic in the pipe 200. A preferential mechanicalcharacteristic may be achieved, such as a strength, stiffness, flexuralrigidity, bending, resonant characteristic, deformation characteristics,failure characteristics or the like. A preferential thermalcharacteristic may be achieved, such as a thermal expansioncharacteristic, thermal insulation characteristic or the like. The localconstructional variation of the pipe wall 202 in the longitudinalportion 204 may be configured to focus a particular behaviouralcharacteristic at said longitudinal portion 204. For example, the localconstructional variation may permit a controlled deformation to beachieved within said longitudinal portion 204, and in some embodimentsto be substantially restricted to said longitudinal portion 204. Suchdeformation may include buckling, longitudinal expansion andcontraction, radial expansion and contraction, torsional deformation,bending or the like. Such deformation may include catastrophic failure,such as axial tensile failure, hoop tensile failure or the like.

A number of possible constructional variations according to the presentinvention may be possible, such as a local variation in modulus ofelasticity, a local variation in second moment of area, a localvariation in coefficient of thermal expansion, a local variation inthermal conductivity, a local variation in material strength, a localvariation in tensile strength, a local variation in hoop strength, alocal variation in geometry, such as wall thickness, a local variationin fibre alignment angle, a local variation in fibre type, a localvariation in matrix type, a local variation in fibre density, a localvariation in composite material pre-stress (for example as defined withreference to FIG. 8), or the like.

Although many different combinations of local variations and uses arepossible within the scope of the present invention, some have beendescribed in detail below for exemplary purposes only.

FIG. 10 provides an illustration of a composite pipe according to anembodiment of the present invention, wherein the pipe defines a riser210 which extends substantially vertically from a seabed 212 towards thesea surface 214. Although not shown, the riser 210 may couple a subseawellhead or manifold to a floating vessel, for example for thecollection of hydrocarbons extracted from a subterranean formation. Inuse the riser 210 will typically be exposed to varying conditions alongits length, particularly in significant water depths. For example, wherethe riser is supported at its upper end, the tension carried by theriser 210 near the surface 214 will be greater than the tension carriednear the seabed 212. Further, the hydrostatic pressure of the sea wateracting externally of the riser 210 will increase with depth, as will theinternal pressure of the product fluid communicated through the riser.As such, the pressure differential internally and externally of theriser 210 will vary with water depth, and particularly will decreasewith depth. Thus, significantly greater mechanical forces, includingaxial tension, hoop forces and the like will be experienced nearer thesurface 214. To accommodate such conditions the composite materialforming the pipe wall is varied to provide increased tensile and burststrengths nearer the surface. This is achieved in the embodiment shownin FIG. 10 by varying the composite material to define a varying wallthickness over the length of the pipe 210, while, in the embodimentshown, maintaining a substantially constant inner diameter.Specifically, the thickness of the pipe wall 216 a at a lowerlongitudinal portion of the riser 210, such as at location A, is thinnerthan the pipe wall 216 b at an upper portion of the riser 210, such asat location B. In this way, the present invention permits an optimumdesign of the riser 210 to be achieved which is optimised or customisedfor the particular application. This provides significant benefits overprior art pipes which are typically globally engineered in accordancewith extreme service conditions, which typically results in a pipe whichis significantly over-engineered for most of its length. As such, thepresent invention may provide suitable pipe products for particularapplications while minimising costs, weight, material usage and thelike.

An alternative embodiment is shown in FIG. 11, in which a riser 220,which also extends vertically from the seabed 222 towards the seasurface 224, defines a constant wall thickness along its length, asdemonstrated by the sectional illustrations of the pipe wall 226 a, 226b taken at lower point A and upper point B. In this embodimentappropriate properties and characteristics of the composite riser 220providing design optimisation for the particular service condition areprovided by a combination of a longitudinal variation in the modulus ofthe composite material and a longitudinal variation in fibre alignmentangle. For example, the composite material within the pipe wall 226 b atlocation B may comprise a higher modulus composite material and a highercombined proportion of near longitudinal fibres (near 0 degreealignment) and near circumferential fibres (near 90 degree alignment)relative to the pipe wall 226 a at location A. As such, the increasedproportion of near longitudinal fibres may accommodate the increasedtensile strength requirements, and the increased proportion of nearcircumferential fibres may accommodate the increased pressuredifferential internally and externally of the riser 220.

It should be noted that the principals of the present invention are notrestricted for use in substantially vertical risers as shown in FIGS. 10and 11. Instead, other riser variations, such as catenary risers may beformed according to the present invention, as illustrated in FIG. 12, inwhich a plurality (although one may be appropriate) of catenary typerisers 221 extend from the seabed 223 to a FPSO vessel 225 floating onthe sea surface 227.

In some embodiments of the invention a composite pipe may be formedwhich includes a longitudinal portion which is configured to accommodatehigh bending moments. Such high bending moments may exist in locationswhere a composite pipe is secured between fixing points which moverelative to each other, such as in riser applications where the riserextends between a fixed seabed location and a floating vessel which issubject to motion, such as heave motion, lateral deviations and thelike. An exemplary embodiment for accommodating high bending moments isdisclosed in FIG. 13, reference to which is now made. Specifically, FIG.13A provides an exemplary plot of bending moment (M) against pipe length(x) from an end 228 of a pipe 230 which is shown in FIG. 13B, whereinthe pipe 230 comprises a pipe wall 232 formed of a composite material.As illustrated, the bending moment is highest at the end 228 of the pipe230, and reduces along its length. To accommodate such a servicecondition the pipe wall 232 includes a maximum thickness at the pipe end228, and reduces thickness along the length of the pipe. In this casethe second moment of area, and thus flexural rigidity of the compositepipe wall will be largest at the pipe end 228, and will reduce along thelength of the pipe in accordance with the reducing bending moment. Inother embodiments the modulus of the composite material and/or the fibrealignment may alternatively, or additionally be modified.

A further alternative embodiment of the present invention is shown inFIG. 14, reference to which is now made. In this embodiment a pipe 240which comprises a pipe wall 242 formed of a composite material includesa longitudinal portion 244 which includes a local variation in theconstruction or make-up of the composite material which focuses orencourages longitudinal bending of the pipe within said longitudinalportion 244. Accordingly, bending within the pipe 240 may be repeatablyand controllably restricted to the longitudinal portion 244. Thisarrangement may permit a hinge effect, for example, to be incorporatedinto the pipe 240. In some exemplary uses this arrangement may beprovided to remove any bending from specific regions of the pipe 240,for example from adjacent regions 246, 248. These adjacent regions 246,248 may be coupled to a further structure, such that when applied forcesencourage longitudinal bending within the pipe 240 bending will beaccommodated and restricted substantially entirely within longitudinalportion 244. This may protect any connection or the like between thepipe and another structure.

In the embodiment shown in FIG. 14 the constructional variation in thecomposite material of the longitudinal portion 244 may be provided in anumber of ways. For example, a variation in fibre alignment may beprovided between sections A-A and B-B. For example, the variation infibre alignment in section B-B may be provided to maintain axial andhoop strength within the pipe 240, but reduce axial stiffness toencourage bending.

The pipe 240 shown in FIG. 14 may be advantageously used as part of apipe bundle, wherein the restricted bending movement to the longitudinalportion 244 may eliminate or substantially minimise interference betweenindividual pipes, permit the pipes to be gathered together in a confinedspace or the like.

For example, a pipe system comprising a plurality of pipes similar tothat pipe 240 shown in FIG. 14 is illustrated in FIG. 15. The pipesystem, generally identified by reference numeral 245 comprises aplurality of pipes (four in the embodiment shown) 240 a-d which convergeto a single location from varying directions, wherein a respectivelongitudinal portion 244 a-d of each pipe 240 a-d permits converging ofthe pipes within a minimal area within minimal interference. Suchconvergence of pipes may occur at a manifold, at a floating vessel orthe like.

Another example is shown in FIG. 16, in which a pipe system 247comprises a plurality of pipes (four in the embodiment shown) 240 e-harranged side-by-side. In this embodiment the respective longitudinalportion 244 e-h facilitates bending of the pipes 240 e-h at a commonlocation.

In an alternative, or supplementary embodiment, a longitudinal portionmay comprise a local constructional variation in composite material tofocus longitudinal expansion and contraction within said longitudinalportion. Such longitudinal expansion and contraction may be a result ofmechanical applied forces, thermal expansion/contraction and the like.Such an embodiment is illustrated in FIG. 17, wherein FIG. 17Ademonstrates a pipe 250 in a contracted configuration, and FIG. 17Bdemonstrates the pipe 250 in an expanded configuration. Specifically, alongitudinal portion 252 of the pipe 250 defines a length l when in acontracted state, and an extended length L when in an expanded state.The longitudinal portion 252 includes a local constructional variationin composite material to permit the longitudinal portion 252 to absorbaxial extension and contraction in the pipe, such as caused by thermalvariations or cycles with minimal lateral deflection or deformation. Inthis embodiment the longitudinal portion 252 may be provided to removeor reduce any expansion and contraction effects in other longitudinalportions of the pipe, such as adjacent portion 254, 256.

A further alternative, or supplementary embodiment of a composite pipeis shown in FIG. 18. In this embodiment the pipe, which is generallyidentified by reference numeral 260, includes a longitudinal portion 262which comprises or defines a local constructional variation in compositematerial to focus lateral buckling, deflection or deformation withinsaid longitudinal portion 262, as illustrated in broken outline. Thismay permit a buckling event, for example by application of a criticalbuckling load, to be restricted within longitudinal portion 262. Acritical buckling load may originate from a service condition of thepipe 260, such as excessive axial thermal expansion or the like. In thispresent embodiment restricting buckling to the longitudinal portion 262may assist in protection of other longitudinal portions, such asadjacent portion 264, 266. In the present embodiment the longitudinalportion may comprise a local constructional variation in the compositematerial to firstly focus buckling at this point, and secondly toaccommodate the lateral buckling deformation without resulting inexceeding the yield point of the material. Further, the localconstructional variation in the composite material within thelongitudinal portion 262 may permit multiple buckling cycles to beaccommodated, while minimising effects of material fatigue and the like.

Another alternative, or supplementary embodiment of a composite pipe isshown in FIG. 19. In this embodiment the pipe, which is generallyidentified by reference numeral 270, includes a longitudinal portion 272which comprises or defines a local constructional variation in compositematerial to focus radial expansion within said longitudinal portion 262,as illustrated in broken outline. Such radial expansion may be caused byinternal pressure. This arrangement may be advantageous in absorption ofthe effects of spikes in internal pressure.

It should be noted that in embodiments of the present invention a localcomposite constructional variation in a longitudinal portion of a pipemay be provided to encourage a particular behavioural characteristic ofthe pipe to accommodate or facilitate improved measurements at saidlongitudinal portion. Such a behavioural characteristic may includebending, axial expansion/contraction, buckling, radial expansion or thelike, such as shown in FIGS. 14 to 19. By permitting or encouraging suchbehaviour, normal pipe movements when in service may be exaggeratedwithin the specified longitudinal portion which may be more appropriateto be monitored by sensing equipment.

Another alternative, or supplementary embodiment of the presentinvention is shown in FIG. 20, reference to which is now made. In thisembodiment a composite pipe is provided, in the exemplary form of ariser 280 which extends vertically from a seabed 282 and upwardly of thesea surface 284. The riser 280 includes a longitudinal portion 286located within an upper region of the riser 280 which includes a localconstructional variation in the composite material to establish a regionwith reduced axial strength. Accordingly, if extreme axial forces areapplied to the riser, for example during extreme weather and seaconditions, failure will be encouraged within longitudinal portion 286,which is conveniently placed near the surface 284 to facilitate easierinspection and repair.

Reference is now made to FIG. 21 in which a diagrammatic illustration ofa composite pipe, generally identified by reference 290, in accordancewith an alternative, or supplementary embodiment of the presentinvention is shown. The pipe 290 is formed of a composite material andincludes a longitudinal section 292 which comprises or defines a localconstructional variation in the composite material which permitsacoustic signals to be transmitted through the pipe wall. Morespecifically, an acoustic apparatus 294 may be positioned on the outersurface of the pipe 290 at the location of the longitudinal portion 292and operated to transmit and/or receive acoustic signals through thepipe wall. In this arrangement the acoustic signals may be used todetermine a property of the pipe 290 and/or a property of a productcontained within the pipe, such as a multiphase property, water-cutproperty, flow property, mass transfer property or the like. The localconstructional variation in composite material within the longitudinalportion 292 may permit the acoustic impedance of the pipe wall to moreclosely match that of, for example, transducers within the acousticapparatus 294, the product within the pipe 290 or the like. For example,the pipe wall may be configured to function as an efficient transducercoupling arrangement.

In other arrangements the pipe wall me be configured to accommodate orsupport other types of signal, such as electromagnetic signals or thelike.

FIG. 22 shows a diagrammatic side view of a pipe system in accordancewith an embodiment of the present invention. Although not illustrated,the pipe system may be configured for multiple applications, such as forsubsea applications. The pipe system comprises two longitudinal steelwall pipe sections 414 and a longitudinal composite wall pipe section416. The composite pipe section may be provided in accordance with anycomposite pipe arrangement defined above. The pipe sections 414, 416 areabutted end to end and the composite pipe section 416 is coupled betweenthe steel wall pipe sections 414 so that a contiguous pipe bore 418 iscreated for the passage of fluid or equipment through the pipe system410. In the embodiment shown, the pipe sections 414, 416 are coupled bya flange connection 420, although it will be understood that anysuitable means for coupling the pipe sections 414, 416 may be used.

The composite pipe section 416 is configured to sustain a greater levelof strain than the metal pipe sections 414 when the pipe system issubject to deformation by a load event. This arrangement, in theembodiments shown, functions to focus the deformation of the pipe systemsubstantially entirely within the composite pipe section 416, thusacting to protect the metal pipe sections 414 from excessive strainsand/or stresses, material fatigue or the like.

In use, the composite pipe section 416 provides a local variation in aproperty of the pipe system along the length thereof. The composite pipesection 416 may be configured to provide a local variation in thetensile strength, compressive strength and/or other property of the pipesystem in order that the pipe system may absorb axial loads, which maybe cyclic axial loads, acting on the pipe system as a result of theenvironmental and/or operational conditions. The composite pipe section416 may also be configured to provide a local variation in the secondmoment of area or other property in order to provide a local variationin the bending stiffness of the pipe system.

In use, the composite pipe section 416 may provide for local expansion,contraction, or bending to absorb the axial loads and reduce oreliminate the occurrence of fatigue, buckling, as may otherwise occur ina pipe system of uniform metal construction. The composite material isconfigured to focus longitudinal expansion and contraction within thecomposite pipe section 416, for example from longitudinal expansion andcontraction as a result of mechanical applied forces, thermalexpansion/contraction and the like.

FIG. 23A illustrates a pipe system in a contracted configuration. FIG.23B illustrates a pipe system in an expanded configuration.

Referring to FIGS. 23A and 23B, a composite pipe section 416 of the pipesystem 410 defines a length l when in a contracted state, and anextended length L when in an expanded state. The composite pipe section416 includes a composite material construction, or a local variation insuch construction, to permit the composite pipe section 416 to absorbaxial extension and contraction in the pipe, such as caused by thermalvariations or cycles with minimal lateral deflection or deformation. Inthis embodiment, the composite pipe section 416 may be provided toremove or reduce any expansion and contraction effects in otherlongitudinal portions of the pipe, such as adjacent pipe sections 414.

A further alternative, or supplementary embodiment is shown in FIG. 24.In this embodiment the composite pipe section 416 comprises a compositematerial construction, or local variation in construction, to focuslateral buckling, deflection or deformation within said composite pipesection 416, as illustrated in broken outline. This may permit a buckingevent, for example by application of a critical buckling load, to berestricted within composite pipe section 416. A critical buckling loadmay originate from a service condition of the pipe system, such as axialthermal expansion or the like. In this present embodiment restrictingbuckling to the composite pipe section 416 may assist in protection ofother pipe sections, such as adjacent sections 414.

In this present embodiment restricting buckling to the composite pipesection 416 may assist in protection of other pipe sections, such asadjacent sections 414. Furthermore, by limiting lateral deviation ordeformation of the pipe system to the composite pipe section, theeffects of a dynamic service condition, such as caused by intermittentoperation, multiphase flow or the like is minimised. For example, thecomposite pipe section 416, by virtue of the composite material, willnot be affected by material fatigue issues, and may be able toaccommodate increased dynamic operational cycles or the like whilemaintaining sufficient integrity. Furthermore, restricting deviation ordeformation within the pipe system to within the composite pipe sectionmay permit absorption of such movement to be achieved by shorter pipelengths which may otherwise be required in continuous metal pipesystems.

Thus, in the present embodiment the composite pipe section 416 maycomprise a local constructional variation in the composite material tofirstly focus buckling at this point, and secondly to accommodate thelateral buckling deformation without resulting in exceeding the yieldpoint of the material. Further, the local constructional variation inthe composite material within the composite pipe section 416 may permitmultiple buckling cycles to be accommodated, while minimising effects ofmaterial fatigue and the like.

A pipe 500 in accordance with an alternative embodiment of the presentinvention is shown in FIG. 25. In this embodiment the pipe 500 includesa pipe wall 502 comprising a composite material formed of at least amatrix and a plurality of reinforcing fibres embedded within the matrix.The matrix extends continuously through the pipe wall 502. A radiallyinner region 504 of the pipe wall 502 is of uniform construction. Anouter region 506 of the pipe wall 502 is of varying construction. Thatis, different sections or portions, such as different longitudinalportions, circumferential portions or the like of the outer region 506may vary in construction. The constructional variation may be providedby any method or arrangement described above in other embodiments.

It should be understood that the embodiments described herein are merelyexemplary, and that various modifications may be made thereto withoutdeparting from the scope of the invention. For example, a pipe may beprovided which has a one or multiple longitudinal portions which includeone or more constructional variations in the composite material to provea number of desired behavioural characteristics. Further, although roundpipes are shown this is not essential, and other cross-sectional shapesmay be possible, such as oval, rectilinear or the like. Further,features of one or more embodiments illustrated above may be providedalone or in combination with the features of any other embodiment. Forexample, a pipe may be provided which as one or more circumferentialvariations, in addition to one or more longitudinal variations.

The invention claimed is:
 1. A pipe having a pipe wall comprising acomposite material formed of at least a matrix and a plurality ofreinforcing fibers embedded within the matrix, wherein a variabletension is applied along the plurality of reinforcing fibers of thecomposite material during manufacture of the pipe to establish a varyinglevel of pre-stress between different regions of the pipe wall, whereinthe level of pre-stress within the composite material of the pipe wallvaries throughout the pipe wall in a radial direction, such that thecomposite material in an outer region or layer of the pipe wallcomprises or defines a different level of pre-stress than the compositematerial in an inner region or layer of the pipe wall.
 2. The pipeaccording to claim 1, wherein the composite material in at least oneregion of the pipe wall comprises or defines at least one of a level ofpre-tension and pre-compression.
 3. The pipe according to claim 1,wherein the pre-stress is applied to the composite material within atleast one region of the pipe wall during manufacture of the pipe,wherein the pre-stress applied during manufacture remains, at leastresidually, within the pipe wall region following manufacture.
 4. Thepipe according to claim 1, wherein the pre-stress within the compositematerial of at least one region of the pipe wall is achieved by applyinga tension to one or more of the reinforcing fibers of the compositeduring manufacture of the pipe.
 5. The pipe according to claim 4,wherein the applied tension introduces a 0.05 to 0.5% strain within oneor more of the reinforcing fibers.
 6. The pipe according to claim 1,wherein the pre-stress within the composite material in at least oneregion of the pipe wall is provided to achieve a desired stress and/orstrain distribution within the pipe wall when the pipe is exposed to ananticipated condition, including at least one of a serviceconfiguration, a storage configuration and a deployment configuration.7. The pipe according to claim 1, wherein the pre-stress within thecomposite material in at least one region of the pipe wall is providedto achieve a desired movement bias of the pipe, including at least oneof bending movement, buckling movement, elongation movement and radialexpansion movement.
 8. The pipe according to claim 1, wherein avariation in pre-stress within the composite material between differentregions of the pipe wall is provided in an abrupt or step-wise manner.9. The pipe according to claim 1, wherein a variation in pre-stresswithin the composite material between different regions of the pipe wallis provided in a gradual or tapered manner.
 10. The pipe according toclaim 1, wherein a variation in pre-stress within the composite materialbetween different regions is provided by a combination of pre-tensionand pre-compression within different regions.
 11. The pipe according toclaim 1, wherein a pre-stress applied within the composite material ofone region of the pipe wall is selected to provide a particular pre-stress in a further region of the pipe wall.
 12. The pipe according toclaim 1, wherein the composite material in an outer region of the pipewall comprises or defines a level of pre-tension, and the compositematerial in an inner region of the pipe wall comprises or defines alevel of pre-compression.
 13. The pipe according to claim 1, wherein alevel of pre-stress within the composite material of the pipe variesthroughout the pipe wall in a longitudinal direction such that thecomposite material in one longitudinal region of the pipe wall comprisesa different level of pre-stress from the composite material in adifferent longitudinal region of the pipe wall.
 14. The pipe accordingto claim 1, wherein the level of pre-stress within the compositematerial of the pipe varies throughout the pipe wall in acircumferential direction such that the composite material in onecircumferential region or segment of the pipe wall comprises a differentlevel of pre-stress from the composite material in a differentcircumferential region or segment of the pipe wall.
 15. The pipeaccording to claim 1, wherein the modulus of the composite material isvaried throughout the pipe wall.
 16. The pipe according to claim 15,wherein the modulus of the composite material is varied by varying themodulus of at least one of the matrix and the reinforcing fibers. 17.The pipe according to claim 15, wherein the modulus of the compositematerial is varied by varying the alignment angle of the reinforcingfibers.
 18. The pipe according to claim 17, wherein one or more fiberslocated within an outer region of the pipe wall define a greater fiberalignment angle than one or more fibers located within an inner regionof the pipe wall.
 19. The pipe according to claim 17, wherein one ormore fibers in an outer region of the pipe wall define a fiber alignmentangle in the region of 75 to 90 degrees, and one or more fibers in aninner region of the pipe wall define a fiber alignment angle in theregion of 65 to 80 degrees.
 20. The pipe according to claim 17, whereinone or more fibers located within an inner region of the pipe walldefine a greater fiber alignment angle than one or more fibers locatedwithin an outer region of the pipe wall.
 21. The pipe according to claim1, wherein at least one circumferential segment of the pipe wallcomprises or defines a local variation in construction to provide alocal variation in a property of the pipe.
 22. The pipe according toclaim 1, wherein at least one longitudinal portion of the pipe wallcomprises or defines a local variation in construction to provide avariation in a property of the pipe.
 23. The pipe according to claim 1,wherein the matrix defines a continuous structure and the fibers arevariably distributed within the continuous matrix structure.
 24. Thepipe according to claim 23, wherein the distribution of the reinforcingfibers varies throughout the continuous matrix in a radial directionthrough the pipe wall.
 25. The pipe according to claim 24, wherein thedistribution of the reinforcing fibers varies from zero at the region ofan inner surface of the pipe wall, and is increased in a directiontowards the outer wall.
 26. The pipe according to claim 1, wherein aradially inner region of the pipe wall defines a uniform level ofpre-stress, and a radially outer region of the pipe wall defines avarying level of pre-stress.
 27. The pipe according to claim 26, whereinthe inner region of the pipe wall is defined by a pre-formed pipestructure or mandrel of uniform pre-stress distribution, and the outerregion of the pipe wall is defined by being formed on the pre-formedmandrel, while including a variation in pre-stress in the radially outerregion.
 28. A method for manufacturing a pipe, comprising: forming apipe wall with a composite material comprising a matrix and a pluralityof reinforcing fibers embedded within the matrix; and applying avariable tension along the plurality of reinforcing fibers of thecomposite material during manufacture of the pipe: and establishing avarying level of pre-stress in the composite material between differentregions of the pipe wall.